Java Fundamental Question and Answers
Encapsulation::
Encapsulation is the mechanism that binds together code and
the data it manipulates and keeps both safe from outside interference and
misuse.
Inheritance :
Inheritance is the process by which one object acquires the
properties of another object.
Polymorphism :
Polymorphism is a feature that allows one interface to be
used for a general class of actions. The specific action is determined by the
exact nature of actions.
Code Blocks :
Two or more statements which is allowed to be grouped into
blocks of code is otherwise called as Code Blocks.This is done by enclosing the
statements between opening and closing curly braces.
Floating-point
numbers:
Floating-point numbers which is also known as real numbers,
are used when evaluating expressions that require fractional precision.
Unicode:
Unicode defines a fully international character set that can
represent all of the characters found in all human languages. It is a unification
of dozens of character sets, such as Latin, Greek, Arabic and many more.
Booleans:
Java has a simple type called boolean, for logical values.
It can have only on of two possible values, true or false.
Casting:
A cast is simply an explicit type conversion. To create a
conversion between two incompatible types, you must use a cast.
Arrays:
An array is a group of like-typed variables that are
referred to by a common name. Arrays offer a convenient means of grouping
related information. Arrays of any type can be created and may have one or more
dimension.
Relational
Operators:
The relational operators determine the relationship that one
operand has to the other. They determine the equality and ordering.
Short-Circuit
Logical Operators:
The secondary versions of the Boolean AND and OR operators
are known as short- circuit logical operators. It is represented by || and
&&..
Switch:
The switch statement is Java’s multiway branch statement. It
provides an easy way to dispatch execution to different parts of your code
based on the value of an experession.
Jump
Statements:
Jump statements are the statements which transfer control to
another part of your program. Java Supports three jump statements: break,
continue, and return.
Instance
Variables:
The data, or variable, defined within a class are called
instance variable.
Introduction to Java Programming
1) The Java interpreter is used for the execution of the
source code.
a) True
b) False
Ans: a.
2) On successful compilation a file with the class extension
is created.
a) True
b) False
Ans: a.
3) The Java source code can be created in a Notepad editor.
a) True
b) False
Ans: a.
4) The Java Program is enclosed in a class definition.
a) True
b) False
Ans: a.
5) What declarations are required for every Java
application?
Ans: A class and the main( ) method declarations.
6) What are the two parts in executing a Java program and
their purposes?
Ans: Two parts in executing a Java program are:
Java Compiler and Java Interpreter.
The Java Compiler is used for compilation and the Java
Interpreter is used for execution of the application.
7) What are the three OOPs principles and define them?
Ans : Encapsulation, Inheritance and Polymorphism are the
three OOPs Principles.
Encapsulation: Is the Mechanism that binds together code and
the data it manipulates, and keeps both safe from outside interference and
misuse.
Inheritance: Is the process by which one object acquires the
properties of another object.
Polymorphism: Is a feature that allows one interface to be
used for a general class of actions.
8) What is a compilation unit?
Ans : Java source code file.
9) What output is displayed as the result of executing the
following statement?
System.out.println("// Looks like a comment.");
1. // Looks like a comment
2. The statement results in a
compilation error
3. Looks like a comment
4. No output is displayed
Ans : a.
10) In order for a source code file, containing the public
class Test, to successfully compile, which of the following must be true?
1. It must have a package
statement
2. It must be named Test.java
3. It must import java.lang
4. It must declare a public
class named Test
Ans : b
11) What are identifiers and what is naming convention?
Ans : Identifiers are used for class names, method names and
variable names. An identifier may be any descriptive sequence of upper case
& lower case letters,numbers or underscore or dollar sign and must not
begin with numbers.
12) What is the return type of program’s main( ) method?
Ans : void
13) What is the argument type of program’s main( ) method?
Ans : string array.
14) Which characters are as first characters of an
identifier?
Ans : A – Z, a – z, _ ,$
15) What are different comments?
Ans : 1) // -- single line comment
2) /* --
*/ multiple line comment
3) /** --
*/ documentation
16) What is the difference between constructor method and
method?
Ans : Constructor will be automatically invoked when an
object is created. Whereas method has to be call explicitly.
17) What is the use of bin and lib in JDK?
Ans : Bin contains all tools such as javac, applet viewer,
awt tool etc., whereas Lib contains all packages and variables
Data types, variables and Arrays
1) What is meant by variable?
Ans: Variables are locations in memory that can hold values.
Before assigning any value to a variable, it must be declared.
2) What are the kinds of variables in Java? What are their
uses?
Ans: Java has three kinds of variables namely, the instance
variable, the local variable and the class variable.
Local variables are used inside blocks as counters or in
methods as temporary variables and are used to store information needed by a
single method.
Instance variables are used to define attributes or the
state of a particular object and are used to store information needed by
multiple methods in the objects.
Class variables are global to a class and to all the
instances of the class and are useful for communicating between different
objects of all the same class or keeping track of global states.
3) How are the variables declared?
Ans: Variables can be declared anywhere in the method
definition and can be initialized during their declaration.They are commonly
declared before usage at the beginning of the definition.
Variables with the same data type can be declared together.
Local variables must be given a value before usage.
4) What are variable types?
Ans: Variable types can be any data type that java supports,
which includes the eight primitive data types, the name of a class or interface
and an array.
5) How do you assign values to variables?
Ans: Values are assigned to variables using the assignment
operator =.
6) What is a literal? How many types of literals are there?
Ans: A literal represents a value of a certain type where
the type describes how that value behaves.There are different types of literals
namely number literals, character literals, boolean literals, string
literals,etc.
Ans: An array is an object that stores a list of items.
8) How do you declare an array?
Ans: Array variable indicates the type of object that the
array holds.
Ex: int arr[];
9) Java supports multidimensional arrays.
a)True
b)False
Ans: a.
10) An array of arrays can be created.
a)True
b)False
Ans: a.
11) What is a string?
Ans: A combination of characters is called as string.
12) Strings are instances of the class String.
a)True
b)False
Ans: a.
13) When a string literal is used in the program, Java
automatically creates instances of the string class.
a)True
b)False
Ans: a.
14) Which operator is to create and concatenate string?
Ans: Addition operator(+).
15) Which of the following declare an array of string
objects?
1. String[ ] s;
2. String [ ]s:
3. String[ s]:
4. String s[ ]:
Ans : a, b and d
16) What is the value of a[3] as the result of the following
array declaration?
1. 1
2. 2
3. 3
4. 4
Ans : d
17) Which of the following are primitive types?
1. byte
2. String
3. integer
4. Float
Ans : a.
18) What is the range of the char type?
1. 0 to 2 16
2. 0 to 2 15
3. 0 to 2 16-1
4. 0 to 2 15-1
Ans. d
19) What are primitive data types?
Ans : byte, short, int, long
float, double
boolean
char
20) What are default values of different primitive types?
Ans :
int - 0
short - 0
byte - 0
long - 0 l
float - 0.0 f
double - 0.0 d
boolean - false
char - null
21) Converting of primitive types to objects can be
explicitly.
a)True
b)False
Ans: b.
22) How do we change the values of the elements of the
array?
Ans : The array subscript expression can be used to change
the values of the elements of the array.
23) What is final varaible?
Ans : If a variable is declared as final variable, then you
can not change its value. It becomes constant.
24) What is static variable?
Ans : Static variables are shared by all instances of a
class.
Operators
1) What are operators and what are the various types of
operators available in Java?
Ans: Operators are special symbols used in expressions. The
following are the types of operators:
Arithmetic operators,
Assignment operators,
Increment & Decrement operators,
Logical operators,
Biwise operators,
Comparison/Relational operators and
Conditional operators
2) The ++ operator is used for incrementing and the --
operator is used for
decrementing.
a)True
b)False
Ans: a.
3) Comparison/Logical operators are used for testing and
magnitude.
a)True
b)False
Ans: a.
4) Character literals are stored as unicode characters.
a)True
b)False
Ans: a.
5) What are the Logical operators?
Ans: OR(|), AND(&), XOR(^) AND NOT(~).
6) What is the % operator?
Ans : % operator is the modulo operator or reminder
operator. It returns the reminder of dividing the first operand by second
operand.
7) What is the value of 111 % 13?
1. 3
2. 5
3. 7
4. 9
Ans : c.
8) Is &&= a valid operator?
Ans : No.
9) Can a double value be cast to a byte?
Ans : Yes
10) Can a byte object be cast to a double value ?
Ans : No. An object cannot be cast to a primitive value.
11) What are order of precedence and associativity?
Ans : Order of precedence the order in which operators are
evaluated in expressions.
Associativity determines whether an expression is evaluated
left-right or right-left.
12) Which Java operator is right associativity?
Ans : = operator.
13) What is the difference between prefix and postfix of --
and ++ operators?
Ans : The prefix form returns the increment or decrement
operation and returns the value of the increment or decrement operation.
The postfix form returns the current value of all of the
expression and then
performs the increment or decrement operation on that value.
14) What is the result of expression 5.45 + "3,2"?
1. The double value 8.6
2. The string
""8.6"
3. The long value 8.
4. The String
"5.453.2"
Ans : d
15) What are the values of x and y ?
x = 5; y = ++x;
Ans : x = 6; y = 6
16) What are the values of x and z?
x = 5; z = x++;
Ans : x = 6; z = 5
Control Statements
1) What are the programming constructs?
Ans:
a) Sequential
b) Selection -- if and switch statements
c) Iteration -- for loop, while loop and do-while loop
2) class conditional {
public static void main(String args[]) {
int i = 20;
int j = 55;
int z = 0;
z = i < j ? i : j; // ternary operator
System.out.println("The value assigned is " + z);
}
}
What is output of the above program?
Ans: The value assigned is 20
3) The switch statement does not require a break.
a)True
b)False
Ans: b.
4) The conditional operator is otherwise known as the
ternary operator.
a)True
b)False
Ans: a.
5) The while loop repeats a set of code while the condition
is false.
a)True
b)False
Ans: b.
6) The do-while loop repeats a set of code atleast once
before the condition is tested.
a)True
b)False
Ans: a.
7) What are difference between break and continue?
Ans: The break keyword halts the execution of the current
loop and forces control out of the loop.
The continue is similar to break, except that instead of
halting the execution of the loop, it starts the next iteration.
8) The for loop repeats a set of statements a certain number
of times until a condition is matched.
a)True
b)False
Ans: a.
9) Can a for statement loop indefintely?
Ans : Yes.
10) What is the difference between while statement and a do
statement/
Ans : A while statement checks at the beginning of a loop to
see whether the next loop iteration should occur.
A do statement checks at the end of a loop to see whether
the next iteration of a loop should occur. The do statement will always execute
the body of a loop at least once.
Introduction to Classes and Methods
1) Which is used to get the value of the instance variables?
Ans: Dot notation.
2) The new operator creates a single instance named class
and returns a reference to that object.
a)True
b)False
Ans: a.
3) A class is a template for multiple objects with similar
features.
a)True
b)False
Ans: a.
4) What is mean by garbage collection?
Ans: When an object is no longer referred to by any
variable, Java automatically reclaims memory used by that object. This is known
as garbage collection.
5) What are methods and how are they defined?
Ans: Methods are functions that operate on instances of
classes in which they are defined.Objects can communicate with each other using
methods and can call methods in other classes.
Method definition has four parts. They are name of the
method, type of object or primitive type the method returns, a list of parameters
and the body of the method. A method's signature is a combination of the first
three parts mentioned above.
6) What is calling method?
Ans: Calling methods are similar to calling or referring to
an instance variable. These methods are accessed using dot notation.
Ex: obj.methodname(param1,param2)
7) Which method is used to determine the class of an object?
Ans: getClass( ) method can be used to find out what class
the belongs to. This class is defined in the object class and is available to
all objects.
8) All the classes in java.lang package are automatically
imported when a program is compiled.
a)True
b)False
Ans: a.
9) How can class be imported to a program?
Ans: To import a class, the import keyword should be used as
shown.;
import classname;
10) How can class be imported from a package to a program?
Ans: import java . packagename . classname (or) import
java.package name.*;
11) What is a constructor?
Ans: A constructor is a special kind of method that
determines how an object is initialized when created.
12) Which keyword is used to create an instance of a class?
Ans: new.
13) Which method is used to garbage collect an object?
Ans: finalize ().
14) Constructors can be overloaded like regular methods.
a)True
b)False
Ans: a.
15) What is casting?
Ans: Casting is bused to convert the value of one type to
another.
16) Casting between primitive types allows conversion of one
primitive type to another.
a)True
b)False
Ans: a.
a)True
b)False
Ans: a.
18) Boolean values can be cast into any other primitive
type.
a)True
b)False
Ans: b.
19) Casting does not affect the original object or value.
a)True
b)False
Ans: a.
20) Which cast must be used to convert a larger value into a
smaller one?
Ans: Explicit cast.
21) Which cast must be used to cast an object to another
class?
Ans: Specific cast.
22) Which of the following features are common to both Java
& C++?
A.The class declaration
b.The access modifiers
c.The encapsulation of data & methods with in objects
d.The use of pointers
Ans: a,b,c.
23) Which of the following statements accurately describe
the use of access modifiers within a class definition?
a.They can be applied to both data & methods
b.They must precede a class's data variables or methods
c.They can follow a class's data variables or methods
d.They can appear in any order
e.They must be applied to data variables first and then to
methods
Ans: a,b,d.
24) Suppose a given instance variable has been declared
private. Can this instance variable be manipulated by methods out side its
class?
a.yes
b.no
Ans: b.
25) Which of the following statements can be used to
describe a public method?
a.It is accessible to all other classes in the hierarchy
b.It is accessablde only to subclasses of its parent class
c.It represents the public interface of its class
d.The only way to gain access to this method is by calling
one of the public class
methods
Ans: a,c.
26) Which of the following types of class members can be
part of the internal part of a class?
a.Public instance variables
b.Private instance variables
c.Public methods
d.Private methods
Ans: b,d.
27) You would use the ____ operator to create a single
instance of a named class.
a.new
b.dot
Ans: a.
28) Which of the following statements correctly describes
the relation between an object and the instance variable it stores?
a.Each new object has its own distinctive set of instance
variables
b.Each object has a copy of the instance variables of its
class
c.the instance variable of each object are seperate from the
variables of other objects
d.The instance variables of each object are stored together
with the variables of other objects
Ans: a,b,c.
29) If no input parameters are specified in a method declaration
then the declaration will include __.
a.an empty set of parantheses
b.the term void
Ans: a.
30) What are the functions of the dot(.) operator?
a.It enables you to access instance variables of any objects
within a class
b.It enables you to store values in instance variables of an
object
c.It is used to call object methods
d.It is to create a new object
Ans: a,b,c.
31) Which of the following can be referenced by this
variable?
a.The instance variables of a class only
b.The methods of a class only
c.The instance variables and methods of a class
Ans: c.
32) The this reference is used in conjunction with
___methods.
a.static
b.non-static
Ans: b.
33) Which of the following operators are used in conjunction
with the this and super references?
a.The new operator
b.The instanceof operator
c.The dot operator
Ans: c.
34) A constructor is automatically called when an object is
instantiated
a. true
b. false
Ans: a.
35) When may a constructor be called without specifying
arguments?
a. When the default constructor is not called
b. When the name of the constructor differs from that of the
class
c. When there are no constructors for the class
Ans: c.
36) Each class in java can have a finalizer method
a. true
b.false
Ans: a.
37) When an object is referenced, does this mean that it has
been identified by the finalizer method for garbage collection?
a.yes
b.no
Ans: b.
38) Because finalize () belongs to the java.lang.Object
class, it is present in all ___.
a.objects
b.classes
c.methods
Ans: b.
39) Identify the true statements about finalization.
a.A class may have only one finalize method
b.Finalizers are mostly used with simple classes
c.Finalizer overloading is not allowed
Ans: a,c.
40) When you write finalize() method for your class, you are
overriding a finalizer inherited from a super class.
a.true
b.false
Ans: a.
41) Java memory management mechanism garbage collects
objects which are no longer referenced
a true
b.false
Ans: a.
42) are objects referenced by a variable candidates for garbage
collection when the variable goes out of scope?
a yes
b. no
Ans: a.
43) Java's garbage collector runs as a ___ priority thread
waiting for __priority threads to relinquish the processor.
a.high
b.low
Ans: a,b.
44) The garbage collector will run immediately when the
system is out of memory
a.true
b.false
Ans: a.
45) You can explicitly drop a object reference by setting
the value of a variable whose data type is a reference type to ___
Ans: null
46) When might your program wish to run the garbage
collecter?
a. before it enters a compute-intense section of code
b. before it enters a memory-intense section of code
c. before objects are finalized
d. when it knows there will be some idle time
Ans: a,b,d
47) For externalizable objects the class is solely
responsible for the external format of its contents
a.true
b.false
Ans: a
48) When an object is stored, are all of the objects that
are reachable from that object stored as well?
a.true
b.false
Ans: a
49) The default__ of objects protects private and trancient
data, and supports the __ of the classes
a.evolution
b.encoding
Ans: b,a.
50) Which are keywords in Java?
a) NULL
b) sizeof
c) friend
d) extends
e) synchronized
Ans : d and e
51) When must the main class and the file name coincide?
Ans :When class is declared public.
52) What are different modifiers?
Ans : public, private, protected, default, static,
trancient, volatile, final, abstract.
53) What are access modifiers?
Ans : public, private, protected, default.
54) What is meant by "Passing by value" and "
Passing by reference"?
Ans : objects – pass by referrence
Methods - pass by value
55) Is a class a subclass of itself?
Ans : A class is a subclass itself.
56) What modifiers may be used with top-level class?
Ans : public, abstract, final.
57) What is an example of polymorphism?
1. Inner class
2. Anonymous classes
3. Method overloading
4. Method overriding
Ans : c
Packages and interface
1) What are packages ? what is use of packages ?
Ans :The package statement defines a name space in which
classes are stored.If you omit the package, the classes are put into the
default package.
Signature... package pkg;
Use: * It specifies to which package the classes
defined in a file belongs to. * Package is both naming and a visibility control
mechanism.
2) What is difference between importing
"java.applet.Applet" and "java.applet.*;" ?
Ans :"java.applet.Applet" will import only the
class Applet from the package java.applet
Where as "java.applet.*" will import all the
classes from java.applet package.
3) What do you understand by package access specifier?
Ans : public: Anything declared as public can be accessed
from anywhere
private: Anything declared in the private can’t be seen
outside of its class.
default: It is visible to subclasses as well as to other
classes in the same package.
4) What is interface? What is use of interface?
Ans : It is similar to class which may contain method’s
signature only but not bodies.
Methods declared in interface are abstract methods. We can
implement many interfaces on a class which support the multiple inheritance.
5) Is it is necessary to implement all methods in an
interface?
Ans : Yes. All the methods have to be implemented.
6) Which is the default access modifier for an interface
method?
Ans : public.
7) Can we define a variable in an interface ?and what type
it should be ?
Ans : Yes we can define a variable in an interface. They are
implicitly final and static.
8) What is difference between interface and an abstract
class?
Ans : All the methods declared inside an Interface are
abstract. Where as abstract class must have at least one abstract method and
others may be concrete or abstract.
In Interface we need not use the keyword abstract for the
methods.
9) By default, all program import the java.lang package.
True/False
Ans : True
10) Java compiler stores the .class files in the path
specified in CLASSPATH
environmental variable.
True/False
Ans : False
11) User-defined package can also be imported just like the
standard packages.
True/False
Ans : True
12) When a program does not want to handle exception, the
______class is used.
Ans : Throws
13) The main subclass of the Exception class is _______
class.
Ans : RuntimeException
14) Only subclasses of ______class may be caught or thrown.
Ans : Throwable
15) Any user-defined exception class is a subclass of the
_____ class.
Ans : Exception
16) The catch clause of the user-defined exception class
should ______ its Base class catch clause.
Ans : Exception
17) A _______ is used to separate the hierarchy of the class
while declaring an Import statement.
Ans : Package
18) All standard classes of Java are included within a
package called _____.
Ans : java.lang
19) All the classes in a package can be simultaneously
imported using ____.
Ans : *
20) Can you define a variable inside an Interface. If no,
why? If yes, how?
Ans.: YES. final and static
21) How many concrete classes can you have inside an
interface?
Ans.: None
22) Can you extend an interface?
Ans.: Yes
23) Is it necessary to implement all the methods of an
interface while implementing the interface?
Ans.: No
24) If you do not implement all the methods of an interface
while implementing , what specifier should you use for the class ?
Ans.: abstract
25) How do you achieve multiple inheritance in Java?
Ans: Using interfaces.
26) How to declare an interface example?
Ans : access class classname implements interface.
27) Can you achieve multiple interface through interface?
a)True
b) false
Ans : a.
28) Can variables be declared in an interface ? If so, what
are the modifiers?
Ans : Yes. final and static are the modifiers can be
declared in an interface.
29) What are the possible access modifiers when implementing
interface methods?
Ans : public.
30) Can anonymous classes be implemented an interface?
Ans : Yes.
31) Interfaces can’t be extended.
a)True
b)False
Ans : b.
32) Name interfaces without a method?
Ans : Serializable, Cloneble & Remote.
33) Is it possible to use few methods of an interface in a
class ? If so, how?
Ans : Yes. Declare the class as abstract.
Exception Handling
1) What is the difference between ‘throw’ and ‘throws’ ?And
it’s application?
Ans : Exceptions that are thrown by java runtime systems can
be handled by Try and catch blocks. With throw exception we can handle the
exceptions thrown by the program itself. If a method is capable of causing an
exception that it does not
handle, it must specify this behavior so the callers of the
method can guard
against that exception.
2) What is the difference between ‘Exception’ and ‘error’ in
java?
Ans : Exception and Error are the subclasses of the
Throwable class. Exception class is used for exceptional conditions that user
program should catch. With exception class we can subclass to create our own
custom exception.
Error defines exceptions that are not excepted to be caught
by you program. Example is Stack Overflow.
3) What is ‘Resource leak’?
Ans : Freeing up other resources that might have been
allocated at the beginning of a method.
4)What is the ‘finally’ block?
Ans : Finally block will execute whether or not an exception
is thrown. If an exception is thrown, the finally block will execute even if no
catch statement match the exception. Any time a method is about to return to
the caller from inside try/catch block, via an uncaught exception or an
explicit return statement, the finally clause is also execute.
5) Can we have catch block with out try block? If so when?
Ans : No. Try/Catch or Try/finally form a unit.
6) What is the difference between the following statements?
Catch (Exception e),
Catch (Error err),
Catch (Throwable t)
Ans :
7) What will happen to the Exception object after exception handling?
Ans : It will go for Garbage Collector. And frees the
memory.
8) How many Exceptions we can define in ‘throws’ clause?
Ans : We can define multiple exceptions in throws clause.
Signature is..
type method-name (parameter-list) throws exception-list
9) The finally block is executed when an exception is
thrown, even if no catch matches it.
True/False
Ans : True
10) The subclass exception should precede the base class
exception when used within the catch clause.
True/False
Ans : True
11) Exceptions can be caught or rethrown to a calling
method.
True/False
Ans : True
12) The statements following the throw keyword in a program
are not executed.
True/False
Ans : True
13) The toString ( ) method in the user-defined exception
class is overridden.
True/False
Ans : True
Multi Threading
1) What are the two types of multitasking?
Ans :
1.process-based
2.Thread-based
2) What are the two ways to create the thread?
Ans :
1.by implementing Runnable
2.by extending Thread
3) What is the signature of the constructor of a thread
class?
Ans : Thread(Runnable threadob,String threadName)
4) What are all the methods available in the Runnable
Interface?
Ans : run()
5) What is the data type for the method isAlive() and this
method is available in which class?
Ans : boolean, Thread
6) What are all the methods available in the Thread class?
Ans :
1.isAlive()
2.join()
3.resume()
4.suspend()
5.stop()
6.start()
7.sleep()
8.destroy()
7) What are all the methods used for Inter Thread
communication and what is the class in which these methods are defined?
Ans :
1. wait(),notify() & notifyall()
2. Object class
8) What is the mechanisam defind by java for the Resources
to be used by only one Thread at a time?
Ans : Synchronisation
9) What is the procedure to own the moniter by many threads?
Ans : not possible
10) What is the unit for 1000 in the below statement?
ob.sleep(1000)
Ans : long milliseconds
11) What is the data type for the parameter of the sleep()
method?
Ans : long
12) What are all the values for the following level?
max-priority
min-priority
normal-priority
Ans : 10,1,5
13) What is the method available for setting the priority?
Ans : setPriority()
14) What is the default thread at the time of starting the
program?
Ans : main thread
15) The word synchronized can be used with only a method.
True/ False
Ans : False
16) Which priority Thread can prompt the lower primary
Thread?
Ans : Higher Priority
17) How many threads at a time can access a monitor?
Ans : one
18) What are all the four states associated in the thread?
Ans : 1. new 2. runnable 3. blocked 4. dead
19) The suspend()method is used to teriminate a thread?
True /False
Ans : False
20) The run() method should necessary exists in clases
created as subclass of thread?
True /False
Ans : True
21) When two threads are waiting on each other and can't
proceed the programe is said to be in a deadlock?
True/False
Ans : True
22) Which method waits for the thread to die ?
Ans : join() method
23) Which of the following is true?
1) wait(),notify(),notifyall() are defined as final &
can be called only from with in a synchronized method
2) Among wait(),notify(),notifyall() the wait() method only
throws IOException
3) wait(),notify(),notifyall() & sleep() are methods of
object class
1. 1
2. 2
3. 3
4. 1 & 2
5. 1,2 & 3
Ans : D
24) Garbage collector thread belongs to which priority?
Ans : low-priority
25) What is meant by timeslicing or time sharing?
Ans : Timeslicing is the method of allocating CPU time to
individual threads in a priority schedule.
26) What is meant by daemon thread? In java runtime, what is
it's role?
Ans : Daemon thread is a low priority thread which runs
intermittently in the background doing the garbage collection operation for the
java runtime system.
Inheritance
1) What is the difference between superclass & subclass?
Ans : A super class is a class that is inherited whereas
subclass is a class that does the inheriting.
2) Which keyword is used to inherit a class?
Ans : extends
3) Subclasses methods can access superclass members/
attributes at all times?
True/False
Ans : False
4) When can subclasses not access superclass members?
Ans : When superclass is declared as private.
5) Which class does begin Java class hierarchy?
Ans : Object class
6) Object class is a superclass of all other classes?
True/False
Ans : True
7) Java supports multiple inheritance?
True/False
Ans : False
8) What is inheritance?
Ans : Deriving an object from an existing class. In the
other words, Inheritance is the process of inheriting all the features from a
class
9) What are the advantages of inheritance?
Ans : Reusability of code and accessibility of variables and
methods of the superclass by subclasses.
10) Which method is used to call the constructors of the
superclass from the subclass?
Ans : super(argument)
11) Which is used to execute any method of the superclass
from the subclass?
Ans : super.method-name(arguments)
12) Which methods are used to destroy the objects created by
the constructor methods?
Ans : finalize()
13) What are abstract classes?
Ans : Abstract classes are those for which instances can’t
be created.
14) What must a class do to implement an interface?
Ans: It must provide all of the methods in the interface and
identify the interface in its implements clause.
15) Which methods in the Object class are declared as final?
Ans : getClass(), notify(), notifyAll(), and wait()
16) Final methods can be overridden.
True/False
Ans : False
17) Declaration of methods as final results in faster
execution of the program?
True/False
Ans: True
18) Final variables should be declared in the beginning?
True/False
Ans : True
19) Can we declare variable inside a method as final variables?
Why?
Ans : Cannot because, local variable cannot be declared as
final variables.
20) Can an abstract class may be final?
Ans : An abstract class may not be declared as final.
21) Does a class inherit the constructors of it's super
class?
Ans: A class does not inherit constructors from any of it's
super classes.
22) What restrictions are placed on method overloading?
Ans: Two methods may not have the same name and argument
list but different return types.
23) What restrictions are placed on method overriding?
Ans : Overridden methods must have the same name , argument
list , and return type. The overriding method may not limit the access of the
method it overridees.The overriding method may not throw any exceptions that
may not be thrown by the overridden method.
24) What modifiers may be used with an inner class that is a
member of an outer class?
Ans : a (non-local) inner class may be declared as public,
protected, private, static, final or abstract.
25) How this() is used with constructors?
Ans: this() is used to invoke a constructor of the same
class
26) How super() used with constructors?
Ans : super() is used to invoke a super class constructor
27) Which of the following statements correctly describes an
interface?
a)It's a concrete class
b)It's a superclass
c)It's a type of abstract class
Ans: c
28) An interface contains __ methods
a)Non-abstract
b)Implemented
c)unimplemented
Ans:c
String Handling
1) Which package does define String and StringBuffer
classes?
Ans : java.lang package.
2) Which method can be used to obtain the length of the
String?
Ans : length( ) method.
3) How do you concatenate Strings?
Ans : By using " + " operator.
4) Which method can be used to compare two strings for
equality?
Ans : equals( ) method.
5) Which method can be used to perform a comparison between
strings that ignores case differences?
Ans : equalsIgnoreCase( ) method.
6) What is the use of valueOf( ) method?
Ans : valueOf( ) method converts data from its internal
format into a human-readable form.
7) What are the uses of toLowerCase( ) and toUpperCase( )
methods?
Ans : The method toLowerCase( ) converts all the characters
in a string from uppercase to
lowercase.
The method toUpperCase( ) converts all the characters in a
string from lowercase to
uppercase.
8) Which method can be used to find out the total allocated
capacity of a StrinBuffer?
Ans : capacity( ) method.
9) Which method can be used to set the length of the buffer
within a StringBuffer object?
Ans : setLength( ).
10) What is the difference between String and StringBuffer?
Ans : String objects are constants, whereas StringBuffer
objects are not.
String class supports constant strings, whereas StringBuffer
class supports growable, modifiable strings.
11) What are wrapper classes?
Ans : Wrapper classes are classes that allow primitive types
to be accessed as objects.
12) Which of the following is not a wrapper class?
1. String
2. Integer
3. Boolean
4. Character
Ans : a.
13) What is the output of the following program?
public class Question {
public static void main(String args[]) {
String s1 = "abc";
String s2 = "def";
String s3 = s1.concat(s2.toUpperCase( ) );
System.out.println(s1+s2+s3);
}
}
1. abcdefabcdef
2. abcabcDEFDEF
3. abcdefabcDEF
4. None of the above
ANS : c.
14) Which of the following methods are methods of the String
class?
1. delete( )
2. append( )
3. reverse( )
4. replace( )
Ans : d.
15) Which of the following methods cause the String object
referenced by s to be changed?
1. s.concat( )
2. s.toUpperCase( )
3. s.replace( )
4. s.valueOf( )
Ans : a and b.
16) String is a wrapper class?
1. True
2. False
Ans : b.
17) If you run the code below, what gets printed out?
String s=new String("Bicycle");
int iBegin=1;
char iEnd=3;
System.out.println(s.substring(iBegin,iEnd));
1. Bic
2. ic
3. icy
4. error: no method matching
substring(int,char)
Ans : b.
18) Given the following declarations
String s1=new String("Hello")
String s2=new String("there");
String s3=new String();
Which of the following are legal operations?
1. s3=s1 + s2;
2. s3=s1 - s2;
3. s3=s1 & s2
4. s3=s1 && s2
Ans : a.
19) Which of the following statements are true?
a)The String class is implemented as a char array, elements
are addressed using the stringname[] convention
b) Strings are a primitive type in Java that overloads the +
operator for concatenation
c) Strings are a primitive type in Java and the StringBuffer
is used as the matching wrapper type
d) The size of a string can be retrieved using the length
property.
Ans : b.
Exploring Java.lang
1) java.lang package is automatically imported into all
programs.
1. True
2. False
Ans : a
2) What are the interfaces defined by java.lang?
Ans : Cloneable, Comparable and Runnable.
3) What are the constants defined by both Flaot and Double
classes?
Ans : MAX_VALUE,
MIN_VALUE,
NaN ,
POSITIVE_INFINITY,
NEGATIVE_INFINITY and
TYPE.
4) What are the constants defined by Byte, Short, Integer
and Long?
Ans : MAX_VALUE,
MIN_VALUE and
TYPE.
5) What are the constants defined by both Float and Double
classes?
Ans : MAX_RADIX,
MIN_RADIX,
MAX_VALUE,
MIN_VALUE and
TYPE.
6) What is the purpose of the Runtime class?
Ans : The purpose of the Runtime class is to provide access
to the Java runtime system.
7) What is the purpose of the System class?
Ans : The purpose of the System class is to provide access
to system resources.
8) Which class is extended by all other classes?
Ans : Object class is extended by all other classes.
9) Which class can be used to obtain design information
about an object?
Ans : The Class class can be used to obtain information
about an object’s design.
10) Which method is used to calculate the absolute value of
a number?
Ans : abs( ) method.
11) What are E and PI?
Ans : E is the base of the natural logarithm and PI is the
mathematical value pi.
12) Which of the following classes is used to perform basic console
I/O?
1. System
2. SecurityManager
3. Math
4. Runtime
Ans : a.
13) Which of the following are true?
1. The Class class is the
superclass of the Object class.
2. The Object class is final.
3. The Class class can be used
to load other classes.
4. The ClassLoader class can be
used to load other classes.
Ans : c and d.
14) Which of the following methods are methods of the Math
class?
1. absolute( )
2. log( )
3. cosine( )
4. sine( )
Ans : b.
15) Which of the following are true about the Error and
Exception classes?
1. Both classes extend
Throwable.
2. The Error class is final and
the Exception class is not.
3. The Exception class is final
and the Error is not.
4. Both classes implement
Throwable.
Ans : a.
16) Which of the following are true?
1. The Void class extends the
Class class.
2. The Float class extends the
Double class.
3. The System class extends the
Runtime class.
4. The Integer class extends
the Number class.
Ans : d.
17) Which of the following will output -4.0
1. System.out.println(Math.floor(-4.7));
2. System.out.println(Math.round(-4.7));
3. System.out.println(Math.ceil(-4.7));
4. System.out.println(Math.Min(-4.7));
Ans : c.
18) Which of the following are valid statements
a) public class MyCalc extends Math
b) Math.max(s);
c) Math.round(9.99,1);
d) Math.mod(4,10);
e) None of the above.
Ans : e.
19) What will happen if you attempt to compile and run the
following code?
Integer ten=new Integer(10);
Long nine=new Long (9);
System.out.println(ten + nine);
int i=1;
System.out.println(i + ten);
1. 19 followed by 20
2. 19 followed by 11
3. Error: Can't convert java
lang Integer
d) 10 followed by 1
Ans : c.
Input/Output: Exploring Java.io
1) What is meant by Stream and what are the types of Streams
and classes of the Streams?
Ans : A Stream is an abstraction that either produces or
consumes information.
There are two types of Streams. They are:
Byte Streams : Byte Streams provide a convenient means for
handling input and output of bytes.
Character Streams : Character Streams provide a convenient
means for handling input and output of characters.
Byte Stream classes : Byte Streams are defined by using two
abstract classes. They are:InputStream and OutputStream.
Character Stream classes : Character Streams are defined by
using two abstract classes. They are : Reader and Writer.
2) Which of the following statements are true?
1. UTF characters are all
8-bits.
2. UTF characters are all
16-bits.
3. UTF characters are all
24-bits.
4. Unicode characters are all
16-bits.
5. Bytecode characters are all
16-bits.
Ans : d.
3) Which of the following statements are true?
1. When you construct an
instance of File, if you do not use the filenaming semantics of the local
machine, the constructor will throw an IOException.
2. When you construct an
instance of File, if the corresponding file does not exist on the local file system,
one will be created.
3. When an instance of File is
garbage collected, the corresponding file on the local file system is deleted.
4. None of the above.
Ans : a,b and c.
4) The File class contains a method that changes the current
working directory.
1. True
2. False
Ans : b.
5) It is possible to use the File class to list the contents
of the current working directory.
1. True
2. False
Ans : a.
6) Readers have methods that can read and return floats and
doubles.
1. True
2. False
Ans : b.
7) You execute the code below in an empty directory. What is
the result?
File f1 = new File("dirname");
File f2 = new File(f1, "filename");
1. A new directory called
dirname is created in the current working directory.
2. A new directory called
dirname is created in the current working directory. A new file called filename
is created in directory dirname.
3. A new directory called
dirname and a new file called filename are created, both in the current working
directory.
4. A new file called filename
is created in the current working directory.
5. No directory is created, and
no file is created.
Ans : e.
8) What is the difference between the Reader/Writer class
hierarchy and the InputStream/OutputStream class hierarchy?
Ans : The Reader/Writer class hierarchy is
character-oriented and the InputStream/OutputStream class hierarchy is
byte-oriented.
9) What is an I/O filter?
Ans : An I/O filter is an object that reads from one stream
and writes to another, usually altering the data in some way as it is passed
from one stream to another.
10) What is the purpose of the File class?
Ans : The File class is used to create objects that provide
access to the files and directories of a local file system.
11) What interface must an object implement before it can be
written to a stream as an object?
Ans : An object must implement the Serializable or
Externalizable interface before it can be written to a stream as an object.
12) What is the difference between the File and
RandomAccessFile classes?
Ans : The File class encapsulates the files and directories
of the local file system. The RandomAccessFile class provides the methods
needed to directly access data contained in any part of a file.
13) What class allows you to read objects directly from a
stream?
Ans : The ObjectInputStream class supports the reading of
objects from input streams.
14) What value does read( ) return when it has reached the
end of a file?
Ans : The read( ) method returns – 1 when it has reached the
end of a file.
15) What value does readLine( ) return when it has reached
the end of a file?
Ans : The readLine( ) method returns null when it has
reached the end of a file.
16) How many bits are used to represent Unicode, ASCII,
UTF-16 and UTF-8 characters?
Ans : Unicode requires 16-bits and ASCII requires 8-bits.
Although the ASCII character set uses only 1-bits, it is usually represented as
8-bits. UTF-8 represents characters using 8, 16 and 18-bit patterns. UTF-16
uses 16-bit and larger bit patterns.
17) Which of the following are true?
1. The InputStream and
OutputStream classes are byte-oriented.
2. The ObjectInputStream and
ObjectOutputStream do not support serialized object input and output.
3. The Reader and Writer
classes are character-oriented.
4. The Reader and Writer
classes are the preferred solution to serialized object output.
Ans : a and c.
18) Which of the following are true about I/O filters?
1. Filters are supported on
input, but not on output.
2. Filters are supported by the
InputStream/OutputStream class hierarchy, but not by the Reader/Writer class
hierarchy.
3. Filters read from one stream
and write to another.
4. A filter may alter data that
is read from one stream and written to another.
Ans : c and d.
19) Which of the following are true?
1. Any Unicode character is
represented using 16-bits.
2. 7-bits are needed to
represent any ASCII character.
3. UTF-8 characters are
represented using only 8-bits.
4. UTF-16 characters are
represented using only 16-bits.
Ans : a and b.
20) Which of the following are true?
1. The Serializable interface is
used to identify objects that may be written to an output stream.
2. The Externalizable interface
is implemented by classes that control the way in which their objects are
serialized.
3. The Serializable interface
extends the Externalizable interface.
4. The Externalizable interface
extends the Serializable interface.
Ans : a, b and d.
21) Which of the following are true about the File class?
1. A File object can be used to
change the current working directory.
2. A File object can be used to
access the files in the current directory.
3. When a File object is
created, a corresponding directory or file is created in the local file system.
4. File objects are used to
access files and directories on the local file system.
5. File objects can be garbage
collected.
6. When a File object is
garbage collected, the corresponding file or directory is deleted.
Ans : b, d and e.
22) How do you create a Reader object from an InputStream
object?
1. Use the static createReader(
) method of InputStream class.
2. Use the static createReader(
) method of Reader class.
3. Create an InputStreamReader
object, passing the InputStream object as an argument to the InputStreamReader
constructor.
4. Create an OutputStreamReader
object, passing the InputStream object as an argument to the OutputStreamReader
constructor.
Ans : c.
23) Which of the following are true?
1. Writer classes can be used
to write characters to output streams using different character encodings.
2. Writer classes can be used
to write Unicode characters to output streams.
3. Writer classes have methods
that support the writing of the values of any Java primitive type to output
streams.
4. Writer classes have methods
that support the writing of objects to output streams.
Ans : a and b.
24) The isFile( ) method returns a boolean value depending
on whether the file object is a file or a directory.
1. True.
2. False.
Ans : a.
25) Reading or writing can be done even after closing the
input/output source.
1. True.
2. False.
Ans : b.
26) The ________ method helps in clearing the buffer.
Ans : flush( ).
27) The System.err method is used to print error message.
1. True.
2. False.
Ans : a.
28) What is meant by StreamTokenizer?
Ans : StreamTokenizer breaks up InputStream into tokens that
are delimited by sets of characters.
It has the constructor : StreamTokenizer(Reader inStream).
Here inStream must be some form of Reader.
29) What is Serialization and deserialization?
Ans : Serialization is the process of writing the state of
an object to a byte stream.
Deserialization is the process of restoring these objects.
30) Which of the following can you perform using the File
class?
a) Change the current directory
b) Return the name of the parent directory
c) Delete a file
d) Find if a file contains text or binary information
Ans : b and c.
31) How can you change the current working directory using
an instance of the File class called FileName?
1. FileName.chdir("DirName").
2. FileName.cd("DirName").
3. FileName.cwd("DirName").
4. The File class does not
support directly changing the current directory.
Ans : d.
Applets
1) What is an Applet? Should applets have constructors?
Ans : Applet is a dynamic and interactive program that runs
inside a Web page displayed by a Java capable browser. We don’t have the
concept of Constructors in Applets.
2) How do we read number information from my applet’s
parameters, given that Applet’s getParameter() method returns a string?
Ans : Use the parseInt() method in the Integer Class, the
Float(String) constructor in the Class Float, or the Double(String) constructor
in the class Double.
3) How can I arrange for different applets on a web page to
communicate with each other?
Ans : Name your applets inside the Applet tag and invoke
AppletContext’s getApplet() method in your applet code to obtain references to
the other applets on the page.
4) How do I select a URL from my Applet and send the browser
to that page?
Ans : Ask the applet for its applet context and invoke
showDocument() on that context object.
Eg. URL targetURL;
String URLString
AppletContext context = getAppletContext();
try{
targetUR L = new URL(URLString);
} catch (Malformed URLException e){
// Code for recover from the exception
}
context. showDocument (targetURL);
5) Can applets on different pages communicate with each
other?
Ans : No. Not Directly. The applets will exchange the
information at one meeting place
either on the local file system or at remote system.
6) How do Applets differ from Applications?
Ans : Appln: Stand Alone
Applet: Needs no explicit installation on local m/c.
Appln: Execution starts with main() method.
Applet: Execution starts with init() method.
Appln: May or may not be a GUI
Applet: Must run within a GUI (Using AWT)
7) How do I determine the width and height of my
application?
Ans : Use the getSize() method, which the Applet class
inherits from the Component
class in the Java.awt package. The getSize() method returns
the size of the applet as
a Dimension object, from which you extract separate width,
height fields.
Eg. Dimension dim = getSize ();
int appletwidth = dim.width ();
8) What is AppletStub Interface?
Ans : The applet stub interface provides the means by which
an applet and the browser communicate. Your code will not typically implement
this interface.
9) It is essential to have both the .java file and the .html
file of an applet in the same directory.
1. True.
2. False.
Ans : 2.
10) The <PARAM> tag contains two attributes namely
_________ and _______.
Ans : Name , value.
11) Passing values to parameters is done in the _________
file of an applet.
Ans : .html.
12) What tags are mandatory when creating HTML to display an
applet
1. name, height, width
2. code, name
3. codebase, height, width
4. code, height, width
Ans : 4.
13) Applet’s getParameter( ) method can be used to get
parameter values.
1. True.
2. False.
Ans : a.
14) What are the Applet’s Life Cycle methods? Explain them?
Ans : init( ) method - Can be called when an applet is first
loaded.
start( ) method - Can be called each time an applet is
started.
paint( ) method - Can be called when the applet is minimized
or refreshed.
stop( ) method - Can be called when the browser moves off
the applet’s page.
destroy( ) method - Can be called when the browser is
finished with the applet.
15) What are the Applet’s information methods?
Ans : getAppletInfo( ) method : Returns a string describing
the applet, its author ,copy
right information, etc.
getParameterInfo( ) method : Returns an array of string
describing the applet’s parameters.
16) All Applets are subclasses of Applet.
1. True.
2. False.
Ans : a.
17) All Applets must import java.applet and java.awt.
1. True.
2. False.
Ans : a.
18) What are the steps involved in Applet development?
Ans : a) Edit a Java source file,
b) Compile your program and
c) Execute the appletviewer, specifying the name of your
applet’s source file.
19) Applets are executed by the console based Java run-time
interpreter.
1. True.
2. False.
Ans : b.
20) Which classes and interfaces does Applet class consist?
Ans : Applet class consists of a single class, the Applet
class and three interfaces: AppletContext,
AppletStub and AudioClip.
21) What is the sequence for calling the methods by AWT for
applets?
Ans : When an applet begins, the AWT calls the following methods,
in this sequence.
1. init( )
2. start( )
3. paint( )
22) When an applet is terminated, the following sequence of
method cals takes place :
1. stop( )
2. destroy( )
23) Which method is used to output a string to an applet?
Ans : drawString ( ) method.
24) Every color is created from an RGB value.
1. True.
2. False
Ans : a.
Event Handling
1) The event delegation model, introduced in release 1.1 of
the JDK, is fully compatible with the event model.
1. True
2. False
Ans : b.
2) A component subclass that has executed enableEvents( ) to
enable processing of a certain kind of event cannot also use an adapter as a
listener for the same kind of event.
1. True
2. False
Ans : b.
3) What is the highest-level event class of the
event-delegation model?
Ans : The java.util.eventObject class is the highest-level
class in the event-delegation hierarchy.
4) What interface is extended by AWT event listeners?
Ans : All AWT event listeners extend the
java.util.EventListener interface.
5) What class is the top of the AWT event hierarchy?
Ans : The java.awt.AWTEvent class is the highest-level class
in the AWT event class hierarchy.
6) What event results from the clicking of a button?
Ans : The ActionEvent event is generated as the result of
the clicking of a button.
7) What is the relationship between an event-listener
interface and an event-adapter class?
Ans : An event-listener interface defines the methods that
must be implemented by an event handler for a particular kind of event. An event
adapter provides a default implementation of an event-listener interface.
8) In which package are most of the AWT events that support
the event-delegation model defined?
Ans : Most of the AWT–related events of the event-delegation
model are defined in the java.awt.event package. The AWTEvent class is defined
in the java.awt package.
9) What is the advantage of the event-delegation model over
the earlier event-inheritance model?
Ans : The event-delegation has two advantages over the
event-inheritance model. They are :
1. It enables event handling by
objects other than the ones that generate the events. This allows a clean
separation between a component’s design and its use.
2. It performs much better in
applications where many events are generated. This performance improvement is
due to the fact that the event-delegation model does not have to repeatedly
process unhandled events, as is the case of the event-inheritance model.
10) What is the purpose of the enableEvents( ) method?
Ans :The enableEvents( ) method is used to enable an event
for a particular object.
11) Which of the following are true?
1. The event-inheritance model
has replaced the event-delegation model.
2. The event-inheritance model
is more efficient than the event-delegation model.
3. The event-delegation model
uses event listeners to define the methods of event-handling classes.
4. The event-delegation model
uses the handleEvent( ) method to support event handling.
Ans : c.
12) Which of the following is the highest class in the
event-delegation model?
1. java.util.EventListener
2. java.util.EventObject
3. java.awt.AWTEvent
4. java.awt.event.AWTEvent
Ans : b.
13) When two or more objects are added as listeners for the
same event, which listener is first invoked to handle the event?
1. The first object that was
added as listener.
2. The last object that was
added as listener.
3. There is no way to determine
which listener will be invoked first.
4. It is impossible to have
more than one listener for a given event.
Ans : c.
14) Which of the following components generate action
events?
1. Buttons
2. Labels
3. Check boxes
4. Windows
Ans : a.
15) Which of the following are true?
1. A TextField object may
generate an ActionEvent.
2. A TextArea object may
generate an ActionEvent.
3. A Button object may generate
an ActionEvent.
4. A MenuItem object may
generate an ActionEvent.
Ans : a,c and d.
16) Which of the following are true?
1. The MouseListener interface
defines methods for handling mouse clicks.
2. The MouseMotionListener
interface defines methods for handling mouse clicks.
3. The MouseClickListener
interface defines methods for handling mouse clicks.
4. The ActionListener interface
defines methods for handling the clicking of a button.
Ans : a and d.
17) Suppose that you want to have an object eh handle the
TextEvent of a TextArea object t. How should you add eh as the event handler
for t?
1. t.addTextListener(eh);
2. eh.addTextListener(t);
3. addTextListener(eh.t);
4. addTextListener(t,eh);
Ans : a.
18) What is the preferred way to handle an object’s events
in Java 2?
1. Override the object’s
handleEvent( ) method.
2. Add one or more event
listeners to handle the events.
3. Have the object override its
processEvent( ) methods.
4. Have the object override its
dispatchEvent( ) methods.
Ans : b.
19) Which of the following are true?
1. A component may handle its
own events by adding itself as an event listener.
2. A component may handle its
own events by overriding its event-dispatching method.
3. A component may not handle
oits own events.
4. A component may handle its
own events only if it implements the handleEvent( ) method.
Ans : a and b.
20) How many types of events are provided by AWT? Explain
them?
Ans : The AWT provides two types of events. They are :
21) Low-level event : A low-level event is the one that
represents a low-level input or window-system occurrence on a visual component
on the screen.
22) Semantic event : Semantic event is defined at a
higher-level to encapsulate the semantics of a user interface component’s
model.
23) A __________ is an object that originates or
"fire" events.
Ans : source.
24) The event listener corresponding to handling keyboard
events is the _________ .
Ans : KeyListener.
25) What are the types of mouse event listeners?
Ans : MouseListener and MouseMotionListener.
26) Which of the following are correct event handling
methods
a) mousePressed(MouseEvent e){}
b) MousePressed(MouseClick e){}
c) functionKey(KeyPress k){}
d) componentAdded(ContainerEvent e){}
Ans : a and d.
27) Which of the following are true?
a) A component may have only one event listener attached at
a time
b) An event listener may be removed from a component
c) The ActionListener interface has no corresponding Adapter
class
d) The processing of an event listener requires a try/catch
block
Ans : b and c.
AWT : windows, graphics and fonts
1) How would you set the color of a graphics context called
g to cyan?
1. g.setColor(Color.cyan);
2. g.setCurrentColor(cyan);
3. g.setColor("Color.cyan");
4. g.setColor("cyan’);
5. g.setColor(new Color(cyan));
Ans : a.
2) The code below draws a line. What color is the line?
g.setColor(Color.red.green.yellow.red.cyan);
g.drawLine(0, 0, 100,100);
1. Red
2. Green
3. Yellow
4. Cyan
5. Black
Ans : d.
3) What does the following code draw?
g.setColor(Color.black);
g.drawLine(10, 10, 10, 50);
g.setColor(Color.RED);
g.drawRect(100, 100, 150, 150);
1. A red vertical line that is
40 pixels long and a red square with sides of 150 pixels
2. A black vertical line that
is 40 pixels long and a red square with sides of 150 pixels
3. A black vertical line that
is 50 pixels long and a red square with sides of 150 pixels
4. A red vertical line that is
50 pixels long and a red square with sides of 150 pixels
5. A black vertical line that
is 40 pixels long and a red square with sides of 100 pixel
Ans : b.
4) Which of the statements below are true?
a) A polyline is always filled.
b) A polyline can not be filled.
c) A polygon is always filled.
d) A polygon is always closed
e) A polygon may be filled or not filled
Ans : b, d and e.
5) What code would you use to construct a 24-point bold
serif font?
1. new Font(Font.SERIF,
24,Font.BOLD);
2. new Font("SERIF",
24, BOLD");
3. new Font("BOLD ",
24,Font.SERIF);
4. new Font("SERIF",
Font.BOLD,24);
5. new Font(Font.SERIF,
"BOLD", 24);
Ans : 4.
6) What does the following paint( ) method draw?
Public void paint(Graphics g) {
g.drawString("question #6",10,0);
}
1. The string "question
#6", with its top-left corner at 10,0
2. A little squiggle coming
down from the top of the component, a little way in from the left edge
Ans : 2.
7) What does the following paint( ) method draw?
Public void paint(Graphics g) {
g.drawString("question #6",10,0);
}
1. A circle at (100, 100) with
radius of 44
2. A circle at (100, 44) with
radius of 100
3. A circle at (100, 44) with
radius of 44
4. The code does not compile
Ans : 4.
8) What is relationship between the Canvas class and the
Graphics class?
Ans : A Canvas object provides access to a Graphics object
via its paint( ) method.
9) What are the Component subclasses that support painting.
Ans : The Canvas, Frame, Panel and Applet classes support
painting.
10) What is the difference between the paint( ) and repaint(
) method?
Ans : The paint( ) method supports painting via a Graphics
object. The repaint( ) method is used to cause paint( ) to be invoked by the
AWT painting method.
11) What is the difference between the Font and FontMetrics
classes?
Ans : The FontMetrics class is used to define
implementation-specific properties, such as ascent and descent, of a Font
object.
12) Which of the following are passed as an argument to the
paint( ) method?
1. A Canvas object
2. A Graphics object
3. An Image object
4. A paint object
Ans : b.
13) Which of the following methods are invoked by the AWT to
support paint and repaint operations?
1. paint( )
2. repaint( )
3. draw( )
4. redraw( )
Ans : a.
14) Which of the following classes have a paint( ) method?
1. Canvas
2. Image
3. Frame
4. Graphics
Ans : a and c.
15) Which of the following are methods of the Graphics
class?
1. drawRect( )
2. drawImage( )
3. drawPoint( )
4. drawString( )
Ans : a, b and d.
16) Which Font attributes are available through the
FontMetrics class?
1. ascent
2. leading
3. case
4. height
Ans : a, b and d.
17) Which of the following are true?
1. The AWT automatically causes
a window to be repainted when a portion of a window has been minimized and then
maximized.
2. The AWT automatically causes
a window to be repainted when a portion of a window has been covered and then
uncovered.
3. The AWT automatically causes
a window to be repainted when application data is changed.
4. The AWT does not support
repainting operations.
Ans : a and b.
18) Which method is used to size a graphics object to fit
the current size of the window?
Ans : getSize( ) method.
19) What are the methods to be used to set foreground and
background colors?
Ans : setForeground( ) and setBackground( ) methods.
20) You have created a simple Frame and overridden the paint
method as follows
public void paint(Graphics g){
g.drawString("Dolly",50,10);
}
What will be the result when you attempt to compile and run
the program?
a) The string "Dolly" will be displayed at the
centre of the frame
b) An error at compilation complaining at the signature of
the paint method
c) The lower part of the word Dolly will be seen at the top
of the form, with the top hidden.
d) The string "Dolly" will be shown at the bottom
of the form
Ans : c.
21) Where g is a graphics instance what will the following
code draw on the screen.
g.fillArc(45,90,50,50,90,180);
a) An arc bounded by a box of height 45, width 90 with a
centre point of 50,50, starting
at an angle of 90 degrees traversing through 180 degrees
counter clockwise.
b) An arc bounded by a box of height 50, width 50, with a centre
point of 45,90 starting
at an angle of 90 degrees traversing through 180 degrees
clockwise.
c) An arc bounded by a box of height 50, width 50, with a
top left at coordinates of 45,
90, starting at 90 degrees and traversing through 180
degrees counter clockwise.
d) An arc starting at 45 degrees, traversing through 90
degrees clockwise bounded by a
box of height 50, width 50 with a centre point of 90, 180.
Ans : c.
22) Given the following code
import java.awt.*;
public class SetF extends Frame{
public static void main(String argv[]){
SetF s = new SetF();
s.setSize(300,200);
s.setVisible(true);
}
}
How could you set the frame surface color to pink
a)s.setBackground(Color.pink);
b)s.setColor(PINK);
c)s.Background(pink);
d)s.color=Color.pink
Ans : a.
AWT: Controls, Layout Managers and Menus
1) What is meant by Controls and what are different types of
controls?
Ans : Controls are componenets that allow a user to interact
with your application.
The AWT supports the following types of controls:
§ Labels
§ Push buttons
§ Check boxes
§ Choice lists
§ Lists
§ Scroll bars
§ Text components
These controls are subclasses of Component.
2) You want to construct a text area that is 80
character-widths wide and 10 character-heights tall. What code do you use?
1. new TextArea(80, 10)
2. new TextArea(10, 80)
Ans: b.
3) A text field has a variable-width font. It is constructed
by calling new TextField("iiiii"). What happens if you change the
contents of the text field to "wwwww"? (Bear in mind that is one of
the narrowest characters, and w is one of the widest.)
1. The text field becomes
wider.
2. The text field becomes
narrower.
3. The text field stays the
same width; to see the entire contents you will have to scroll by using the ß
and à keys.
4. The text field stays the same
width; to see the entire contents you will have to scroll by using the text
field’s horizontal scroll bar.
Ans : c.
4) The CheckboxGroup class is a subclass of the Component
class.
1. True
2. False
Ans : b.
5) What are the immediate super classes of the following
classes?
1. a) Container class
2. b) MenuComponent class
3. c) Dialog class
4. d) Applet class
5. e) Menu class
Ans : a) Container - Component
b) MenuComponent - Object
c) Dialog - Window
d) Applet - Panel
e) Menu - MenuItem
6) What are the SubClass of Textcomponent Class?
Ans : TextField and TextArea
7) Which method of the component class is used to set the
position and the size of a component?
Ans : setBounds()
8) Which TextComponent method is used to set a TextComponent
to the read-only state?
Ans : setEditable()
9) How can the Checkbox class be used to create a radio
button?
Ans : By associating Checkbox objects with a CheckboxGroup.
10) What Checkbox method allows you to tell if a Checkbox is
checked?
Ans : getState()
11) Which Component method is used to access a component's
immediate Container?
1. getVisible()
2. getImmediate
3. getParent()
4. getContainer
Ans : c.
12) What methods are used to get and set the text label
displayed by a Button object?
Ans : getLabel( ) and setLabel( )
13) What is the difference between a Choice and a List?
Ans : A Choice is displayed in a compact form that requires
you to pull it down to see the list of available choices. Only one item may be
selected from a Choice.
A List may be displayed in such a way that several List
items are visible. A List supports the selection of one or more List items.
14) Which Container method is used to cause a container to
be laid out and redisplayed?
Ans : validate( )
15) What is the difference between a Scollbar and a
Scrollpane?
Ans : A Scrollbar is a Component, but not a Container.
A Scrollpane is a Container and handles its own events and
performs its own
scrolling.
16) Which Component subclass is used for drawing and
painting?
Ans : Canvas.
17) Which of the following are direct or indirect subclasses
of Component?
1. Button
2. Label
3. CheckboxMenuItem
4. Toolbar
5. Frame
Ans : a, b and e.
18) Which of the following are direct or indirect subclasses
of Container?
1. Frame
2. TextArea
3. MenuBar
4. FileDialog
5. Applet
Ans : a,d and e.
19) Which method is used to set the text of a Label object?
1. setText( )
2. setLabel( )
3. setTextLabel( )
4. setLabelText( )
Ans : a.
20) Which constructor creates a TextArea with 10 rows and 20
columns?
1. new TextArea(10, 20)
2. new TextArea(20, 10)
3. new TextArea(new Rows(10),
new columns(20))
4. new TextArea(200)
Ans : a.
(Usage is TextArea(rows, columns)
21) Which of the following creates a List with 5 visible
items and multiple selection enabled?
1. new List(5, true)
2. new List(true, 5)
3. new List(5, false)
4. new List(false,5)
Ans : a.
[Usage is List(rows, multipleMode)]
22) Which are true about the Container class?
1. The validate( ) method is
used to cause a Container to be laid out and redisplayed.
2. The add( ) method is used to
add a Component to a Container.
3. The getBorder( ) method
returns information about a Container’s insets.
4. The getComponent( ) method
is used to access a Component that is contained in a Container.
Ans : a, b and d.
23) Suppose a Panel is added to a Frame and a Button is
added to the Panel. If the Frame’s font is set to 12-point TimesRoman, the
Panel’s font is set to 10-point TimesRoman, and the Button’s font is not set,
what font will be used to dispaly the Button’s label?
1. 12-point TimesRoman
2. 11-point TimesRoman
3. 10-point TimesRoman
4. 9-point TimesRoman
Ans : c.
24) A Frame’s background color is set to Color.Yellow, and a
Button’s background color is to Color.Blue. Suppose the Button is added to a
Panel, which is added to the Frame. What background color will be used with the
Panel?
1. Colr.Yellow
2. Color.Blue
3. Color.Green
4. Color.White
Ans : a.
25) Which method will cause a Frame to be displayed?
1. show( )
2. setVisible( )
3. display( )
4. displayFrame( )
Ans : a and b.
26) All the componenet classes and container classes are
derived from _________ class.
Ans : Object.
27) Which method of the container class can be used to add
components to a Panel.
Ans : add ( ) method.
28) What are the subclasses of the Container class?
Ans : The Container class has three major subclasses. They
are :
1. Window
2. Panel
3. ScrollPane
29) The Choice component allows multiple selection.
1. True.
2. False.
Ans : b.
30) The List component does not generate any events.
1. True.
2. False.
Ans : b.
31) Which components are used to get text input from the
user.
Ans : TextField and TextArea.
32) Which object is needed to group Checkboxes to make them
exclusive?
Ans : CheckboxGroup.
33) Which of the following components allow multiple
selections?
1. Non-exclusive Checkboxes.
2. Radio buttons.
3. Choice.
4. List.
Ans : a and d.
34) What are the types of Checkboxes and what is the
difference between them?
Ans : Java supports two types of Checkboxes. They are :
Exclusive and Non-exclusive.
In case of exclusive Checkboxes, only one among a group of
items can be selected at a time. I f an item from the group is selected, the
checkbox currently checked is deselected and the new selection is highlighted.
The exclusive Checkboxes are also called as Radio buttons.
The non-exclusive checkboxes are not grouped together and
each one can be selected independent of the other.
35) What is a Layout Manager and what are the different
Layout Managers available in java.awt and what is the default Layout manager
for the panal and the panal subclasses?
Ans: A layout Manager is an object that is used to organize
components in a container.
The different layouts available in java.awt are :
FlowLayout, BorderLayout, CardLayout, GridLayout and GridBag
Layout.
The default Layout Manager of Panal and Panal sub classes is
FlowLayout".
36) Can I exert control over the size and placement of
components in my interface?
Ans : Yes.
myPanal.setLayout(null);
myPanal.setbounds(20,20,200,200);
37) Can I add the same component to more than one container?
Ans : No. Adding a component to a container automatically
removes it from any previous parent(container).
38) How do I specify where a window is to be placed?
Ans : Use setBounds, setSize, or setLocation methods to
implement this.
setBounds(int x, int y, int width, int height)
setBounds(Rectangle r)
setSize(int width, int height)
setSize(Dimension d)
setLocation(int x, int y)
setLocation(Point p)
39) How can we create a borderless window?
Ans : Create an instance of the Window class, give it a
size, and show it on the screen.
eg. Frame aFrame = ......
Window aWindow = new Window(aFrame);
aWindow.setLayout(new FlowLayout());
aWindow.add(new Button("Press Me"));
aWindow.getBounds(50,50,200,200);
aWindow.show();
40) Can I create a non-resizable windows? If so, how?
Ans: Yes. By using setResizable() method in class Frame.
41) What is the default Layout Manager for the Window and
Window subclasses (Frame,Dialog)?
Ans : BorderLayout().
42) How are the elements of different layouts organized?
Ans : FlowLayout : The elements of a FlowLayout are
organized in a top to bottom, left to right fashion.
BorderLayout : The elements of a BorderLayout are organized
at the
borders (North, South, East and West) and the center of a
container.
CardLayout : The elements of a CardLayout are stacked, one
on top of the other, like a deck of cards.
GridLayout : The elements of a GridLayout are of equal size
and are laid out using the square of a grid.
GridBagLayout : The elements of a GridBagLayout are
organized according to a grid.However, the elements are of different sizes and
may occupy
more than one row or column of the grid. In addition, the
rows and columns may have different sizes.
43) Which containers use a BorderLayout as their default
layout?
Ans : The Window, Frame and Dialog classes use a
BorderLayout as their default layout.
44) Which containers use a FlowLayout as their default
layout?
Ans : The Panel and the Applet classes use the FlowLayout as
their default layout.
45) What is the preferred size of a component?
Ans : The preferred size of a component size that will allow
the component to display normally.
46) Which method is method to set the layout of a container?
1. startLayout( )
2. initLayout( )
3. layoutContainer( )
4. setLayout( )
Ans : d.
47) Which method returns the preferred size of a component?
1. getPreferredSize( )
2. getPreferred( )
3. getRequiredSize( )
4. getLayout( )
Ans : a.
48) Which layout should you use to organize the components
of a container in a tabular form?
1. CardLayout
2. BorederLayout
3. FlowLayout
4. GridLayout
Ans : d.
49) An application has a frame that uses a Border layout
manager. Why is it probably not a good idea to put a vertical scroll bar at
North in the frame?
1. The scroll bar’s height
would be its preferred height, which is not likely to be enough.
2. The scroll bar’s width would
be the entire width of the frame, which would be much wider than necessary.
3. Both a and b.
4. Neither a nor b. There is no
problem with the layout as described.
Ans : c.
50) What is the default layouts for a applet, a frame and a
panel?
Ans : For an applet and a panel, Flow layout is the default
layout, whereas Border layout is default layout for a frame.
51) If a frame uses a Grid layout manager and does not
contain any panels, then all the components within the frame are the same width
and height.
1. True
2. False.
Ans : a.
52) If a frame uses its default layout manager and does not
contain any panels, then all the components within the frame are the same width
and height.
1. True
2. False.
Ans : b.
53) With a Border layout manager, the component at Center
gets all the space that is left over, after the components at North and South
have been considered.
1. True
2. False
Ans : b.
54) An Applet has its Layout Manager set to the default of
FlowLayout. What code would be the correct to change to another Layout Manager?
1. setLayoutManager(new
GridLayout());
2. setLayout(new
GridLayout(2,2));
3. setGridLayout(2,2,))
4. setBorderLayout();
Ans : b.
55) How do you indicate where a component will
be positioned using Flowlayout?
a) North, South,East,West
b) Assign a row/column grid reference
c) Pass a X/Y percentage parameter to the add method
d) Do nothing, the FlowLayout will position the component
Ans :d.
56) How do you change the current layout manager
for a container?
a) Use the setLayout method
b) Once created you cannot change the current layout manager
of a component
c) Use the setLayoutManager method
d) Use the updateLayout method
Ans :a.
57)When using the GridBagLayout manager, each new component
requires a new instance of the GridBagConstraints class. Is this statement true
or false?
a) true
b) false
Ans : b.
58) Which of the following statements are true?
a)The default layout manager for an Applet is FlowLayout
b) The default layout manager for an application is
FlowLayout
c) A layout manager must be assigned to an Applet before the
setSize method is called
d) The FlowLayout manager attempts to honor the preferred
size of any components
Ans : a and d.
59) Which method does display the messages whenever there is
an item selection or deselection of the CheckboxMenuItem menu?
Ans : itemStateChanged method.
60) Which is a dual state menu item?
Ans : CheckboxMenuItem.
61) Which method can be used to enable/diable a checkbox
menu item?
Ans : setState(boolean).
62) Which of the following may a menu contain?
1. A separator
2. A check box
3. A menu
4. A button
5. A panel
Ans : a and c.
63) Which of the following may contain a menu bar?
1. A panel
2. A frame
3. An applet
4. A menu bar
5. A menu
Ans : b
64) What is the difference between a MenuItem and a
CheckboxMenuItem?
Ans : The CheckboxMenuItem class extends the MenuItem class
to support a menu item
that may be checked or unchecked.
65) Which of the following are true?
1. A Dialog can have a MenuBar.
2. MenuItem extends Menu.
3. A MenuItem can be added to a
Menu.
4. A Menu can be added to a
Menu.
Ans : c and d.
Utility Package
1) What is the Vector class?
ANSWER : The Vector class provides the
capability to implement a growable array of objects.
2) What is the Set interface?
ANSWER : The Set interface provides methods for
accessing the elements of a finite mathematical set.Sets do not allow duplicate
elements.
3) What is Dictionary class?
ANSWER : The Dictionary class is the abstarct
super class of Hashtable and Properties class.Dictionary provides the abstarct
functions used to store and retrieve objects by key-value.This class allows any
object to be used as a key or value.
4) What is the Hashtable class?
ANSWER : The Hashtable class implements a hash
table data structure. A hash table indexes and stores objects in a dictionary
using hash codes as the objects' keys. Hash codes are integer values that
identify objects.
5) What is the Properties class?
Answer : The properties class is a subclass of
Hashtable that can be read from or written to a stream.It also provides the
capability to specify a set of default values to be used if a specified key is
not found in the table. We have two methods load() and save().
6) What changes are needed to make the following prg to
compile?
import java.util.*;
class Ques{
public static void main (String args[]) {
String s1 = "abc";
String s2 = "def";
Vector v = new Vector();
v.add(s1);
v.add(s2);
String s3 = v.elementAt(0) + v.elementAt(1);
System.out.println(s3);
}
}
A) Declare Ques as public
B) Cast v.elementAt(0) to a String
C) Cast v.elementAt(1) to an Object.
D) Import java.lang
ANSWER : B) Cast v.elementAt(0) to a String
7) What is the output of the prg.
import java.util.*;
class Ques{
public static void main (String args[]) {
String s1 = "abc";
String s2 = "def";
Stack stack = new Stack();
stack.push(s1);
stack.push(s2);
try{
String s3 = (String) stack.pop() + (String) stack.pop() ;
System.out.println(s3);
}catch (EmptyStackException ex){}
}
}
A) abcdef
B) defabc
C) abcabc
D) defdef
ANSWER : B) defabc
9) Which of the following may have duplicate elements?
A)Collection
B) List
C) Map
D) Set
ANSWER : A and B Neither a Map nor a Set may
have duplicate elements.
10) Can null value be added to a List?
ANSWER : Yes.A Null value may be added to any
List.
11) What is the output of the following prg.
import java.util.*;
class Ques{
public static void main (String args[]) {
HashSet set = new HashSet();
String s1 = "abc";
String s2 = "def";
String s3 = "";
set.add(s1);
set.add(s2);
set.add(s1);
set.add(s2);
Iterator i = set.iterator();
while(i.hasNext())
{
s3 += (String) i.next();
}
System.out.println(s3);
}
}
A) abcdefabcdef B) defabcdefabc C) fedcbafedcba D) defabc
ANSWER : D) defabc. Sets may not have duplicate
elements.
12) Which of the following java.util classes support
internationalization?
A) Locale B) ResourceBundle C) Country D) Language
ANSWER : A and B . Country and Language are not
java.util classes.
13) What is the ResourceBundle?
1. The ResourceBundle class
also supports internationalization.
ResourceBundle subclasses are used to store locale-specific
resources that can be loaded by a program to tailor the program's appearence to
the paticular locale in which it is being run. Resource Bundles provide the
capability to isolate a program's locale-specific resources in a standard and
modular manner.
14) How are Observer Interface and Observable class, in
java.util package, used?
ANSWER : Objects that subclass the Observable
class maintain a list of Observers. When an Observable object is updated it
invokes the update() method of each of its observers to notify the observers
that it has changed state. The Observer interface is implemented by objects
that observe Observable objects.
15) Which java.util classes and interfaces support event
handling?
ANSWER : The EventObject class and the
EventListener interface support event processing.
16) Does java provide standard iterator functions for
inspecting a collection of objects?
ANSWER : The Enumeration interface in the
java.util package provides a framework for stepping once through a collection
of objects. We have two methods in that interface.
public interface Enumeration {
boolean hasMoreElements();
Object nextElement();
}
17) The Math.random method is too limited for my needs-
How can I generate random numbers more flexibly?
ANSWER : The random method in Math class provide
quick, convienient access to random numbers, but more power and flexibility use
the Random class in the java.util package.
double doubleval = Math.random();
The Random class provide methods returning float, int,
double, and long values.
nextFloat() // type float; 0.0 <= value < 1.0
nextDouble() // type double; 0.0 <= value < 1.0
nextInt() // type int; Integer.MIN_VALUE <= value <=
Integer.MAX_VALUE
nextLong() // type long; Long.MIN_VALUE <= value <=
Long.MAX_VALUE
nextGaussian() // type double; has
Gaussian("normal") distribution with mean 0.0 and standard deviation
1.0)
Eg. Random r = new Random();
float floatval = r.nextFloat();
18) How can we get all public methods of an object
dynamically?
ANSWER : By using getMethods(). It return an
array of method objects corresponding to the public methods of this class.
getFields() returns an array of Filed objects corresponding
to the public Fields(variables) of this class.
getConstructors() returns an array of constructor objects
corresponding to the public constructors of this class.
JDBC
1) What are the steps involved in establishing a
connection?
ANSWER : This involves two steps: (1) loading
the driver and (2) making the connection.
2) How can you load the drivers?
ANSWER : Loading the driver or drivers you want
to use is very simple and involves just one line of code. If, for example, you
want to use the JDBC-ODBC Bridge driver, the following code will load it:
Eg.
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Your driver documentation will give you the class name to
use. For instance, if the class name is jdbc.DriverXYZ , you would load the
driver with the following line of code:
Eg.
Class.forName("jdbc.DriverXYZ");
3) What Class.forName will do while loading drivers?
ANSWER : It is used to create an instance of a
driver and register it with the DriverManager.
When you have loaded a driver, it is available for making a
connection with a DBMS.
4) How can you make the connection?
ANSWER : In establishing a connection is to have
the appropriate driver connect to the DBMS. The following line of code
illustrates the general idea:
Eg.
String url = "jdbc:odbc:Fred";
Connection con = DriverManager.getConnection(url,
"Fernanda", "J8");
5) How can you create JDBC statements?
ANSWER : A Statement object is what sends your
SQL statement to the DBMS. You simply create a Statement object and then
execute it, supplying the appropriate execute method with the SQL statement you
want to send. For a SELECT statement, the method to use is executeQuery. For
statements that create or modify tables, the method to use is executeUpdate.
Eg.
It takes an instance of an active connection to create a
Statement object. In the following example, we use our Connection object con to
create the Statement object stmt :
Statement stmt = con.createStatement();
6) How can you retrieve data from the ResultSet?
ANSWER : Step 1.
JDBC returns results in a ResultSet object, so we need to
declare an instance of the class ResultSet to hold our results. The following
code demonstrates declaring the ResultSet object rs.
Eg.
ResultSet rs = stmt.executeQuery("SELECT COF_NAME,
PRICE FROM COFFEES");
Step2.
String s = rs.getString("COF_NAME");
The method getString is invoked on the ResultSet object rs ,
so getString will retrieve (get) the value stored in the column COF_NAME in the
current row of rs
7) What are the different types of Statements?
ANSWER : 1.Statement (use createStatement
method) 2. Prepared Statement (Use prepareStatement method) and 3. Callable
Statement (Use prepareCall)
8) How can you use PreparedStatement?
ANSWER : This special type of statement is
derived from the more general class, Statement.If you want to execute a
Statement object many times, it will normally reduce execution time to use a
PreparedStatement object instead.
The advantage to this is that in most cases, this SQL
statement will be sent to the DBMS right away, where it will be compiled. As a
result, the PreparedStatement object contains not just an SQL statement, but an
SQL statement that has been precompiled. This means that when the
PreparedStatement is executed, the DBMS can just run the PreparedStatement 's
SQL statement without having to compile it first.
Eg.
PreparedStatement updateSales =
con.prepareStatement("UPDATE COFFEES SET SALES = ? WHERE COF_NAME LIKE
?");
9) What setAutoCommit does?
ANSWER : When a connection is created, it is in
auto-commit mode. This means that each individual SQL statement is treated as a
transaction and will be automatically committed right after it is executed. The
way to allow two or more statements to be grouped into a transaction is to
disable auto-commit mode
Eg.
con.setAutoCommit(false);
Once auto-commit mode is disabled, no SQL statements will be
committed until you call the method commit explicitly.
Eg.
con.setAutoCommit(false);
PreparedStatement updateSales = con.prepareStatement(
"UPDATE COFFEES SET SALES = ? WHERE COF_NAME LIKE
?");
updateSales.setInt(1, 50);
updateSales.setString(2, "Colombian");
updateSales.executeUpdate();
PreparedStatement updateTotal =
con.prepareStatement("UPDATE COFFEES SET TOTAL = TOTAL + ? WHERE COF_NAME LIKE
?");
updateTotal.setInt(1, 50);
updateTotal.setString(2, "Colombian");
updateTotal.executeUpdate();
con.commit();
con.setAutoCommit(true);
10) How to call a Strored Procedure from JDBC?
ANSWER : The first step is to create a
CallableStatement object. As with Statement an and PreparedStatement objects,
this is done with an open Connection
object. A CallableStatement object contains a call to a
stored procedure;
Eg.
CallableStatement cs = con.prepareCall("{call
SHOW_SUPPLIERS}");
ResultSet rs = cs.executeQuery();
11) How to Retrieve Warnings?
ANSWER : SQLWarning objects are a subclass of
SQLException that deal with database access warnings. Warnings do not stop the
execution of an application, as exceptions do; they simply alert the user that
something did not happen as planned.
A warning can be reported on a Connection object, a
Statement object (including PreparedStatement and CallableStatement objects),
or a ResultSet object. Each of these classes has a getWarnings method, which
you must invoke in order to see the first warning reported on the calling
object
Eg.
SQLWarning warning = stmt.getWarnings();
if (warning != null) {
System.out.println("\n---Warning---\n");
while (warning != null) {
System.out.println("Message: " +
warning.getMessage());
System.out.println("SQLState: " +
warning.getSQLState());
System.out.print("Vendor error code: ");
System.out.println(warning.getErrorCode());
System.out.println("");
warning = warning.getNextWarning();
}
}
12) How can you Move the Cursor in Scrollable Result Sets
?
ANSWER : One of the new features in the JDBC 2.0
API is the ability to move a result set's cursor backward as well as forward.
There are also methods that let you move the cursor to a particular row and
check the position of the cursor.
Eg.
Statement stmt =
con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_READ_ONLY);
ResultSet srs = stmt.executeQuery("SELECT COF_NAME,
PRICE FROM COFFEES");
The first argument is one of three constants added to the
ResultSet API to indicate the type of a ResultSet object: TYPE_FORWARD_ONLY,
TYPE_SCROLL_INSENSITIVE , and TYPE_SCROLL_SENSITIVE .
The second argument is one of two ResultSet constants for
specifying whether a result set is read-only or updatable: CONCUR_READ_ONLY and
CONCUR_UPDATABLE . The point to remember here is that if you specify a type,
you must also specify whether it is read-only or updatable. Also, you must
specify the type first, and because both parameters are of type int , the
compiler will not complain if you switch the order.
Specifying the constant TYPE_FORWARD_ONLY creates a
nonscrollable result set, that is, one in which the cursor moves only forward.
If you do not specify any constants for the type and updatability of a
ResultSet object, you will automatically get one that is TYPE_FORWARD_ONLY and
CONCUR_READ_ONLY
13) What’s the difference between TYPE_SCROLL_INSENSITIVE
, and TYPE_SCROLL_SENSITIVE?
ANSWER : You will get a scrollable ResultSet
object if you specify one of these ResultSet constants.The difference between
the two has to do with whether a result set reflects changes that are made to
it while it is open and whether certain methods can be called to detect these
changes. Generally speaking, a result set that is TYPE_SCROLL_INSENSITIVE does
not reflect changes made while it is still open and one that is
TYPE_SCROLL_SENSITIVE does. All three types of result sets will make changes
visible if they are closed and then reopened
Eg.
Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
ResultSet srs = stmt.executeQuery("SELECT COF_NAME,
PRICE FROM COFFEES");
srs.afterLast();
while (srs.previous()) {
String name = srs.getString("COF_NAME");
float price = srs.getFloat("PRICE");
System.out.println(name + " " + price);
}
14) How to Make Updates to Updatable Result Sets?
ANSWER : Another new feature in the JDBC 2.0 API
is the ability to update rows in a result set using methods in the Java
programming language rather than having to send an SQL command. But before you
can take advantage of this capability, you need to create a ResultSet object
that is updatable. In order to do this, you supply the ResultSet constant
CONCUR_UPDATABLE to the createStatement method.
Eg.
Connection con =
DriverManager.getConnection("jdbc:mySubprotocol:mySubName");
Statement stmt =
con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_UPDATABLE);
ResultSet uprs = stmt.executeQuery("SELECT COF_NAME,
PRICE FROM COFFEES");
Networking Concepts
1) The API doesn't list any constructors for InetAddress-
How do I create an InetAddress instance?
ANSWER : In case of InetAddress the three
methods getLocalHost, getByName, getByAllName can be used to create instances.
E.g.
InetAddress add1;
InetAddress add2;
try{
add1 = InetAddress.getByName("java.sun.com");
add2 = InetAddress.getByName("199.22.22.22");
}catch(UnknownHostException e){}
2) Is it possible to get the Local host IP?
ANSWER : Yes. Use InetAddress's getLocalHost
method.
3) What's the Factory Method?
ANSWER : Factory methods are merely a convention
whereby static methods in a class return an instance of that class. The
InetAddress class has no visible constructors. To create an InetAddress object,
you have to use one of the available factory methods. In InetAddress the three
methods getLocalHost, getByName, getByAllName can be used to create instances of
InetAddress.
4) What’s the difference between TCP and UDP?
ANSWER : These two protocols differ in the way
they carry out the action of communicating. A TCP protocol establishes a two
way connection between a pair of computers, while the UDP protocol is a one-way
message sender. The common analogy is that TCP is like making a phone call and
carrying on a two-way communication, while UDP is like mailing a letter.
5) What is the Proxy Server?
ANSWER : A proxy server speaks the client side
of a protocol to another server. This is often required when clients have
certain restrictions on which servers they can connect to. And when several
users are hitting a popular web site, a proxy server can get the contents of
the web server's popular pages once, saving expensive internetwork transfers
while providing faster access to those pages to the clients.
Also, we can get multiple connections for a single server.
6) What are the seven layers of OSI model?
ANSWER : Application, Presentation, Session,
Transport, Network, DataLink, Physical Layer.
7) What Transport Layer does?
ANSWER : It ensures that the mail gets to its
destination. If a packet fails to get its destination, it handles the process
of notifying the sender and requesting that another packet be sent.
8) What is DHCP?
ANSWER : Dynamic Host Configuration Protocol, a
piece of the TCP/IP protocol suite that handles the automatic assignment of IP
addresses to clients.
9) What is SMTP?
ANSWER : Simple Mail Transmission Protocol, the
TCP/IP Standard for Internet mails. SMTP exchanges mail between servers;
contrast this with POP, which transmits mail between a server and a client.
10) In OSI N/w architecture, the dialogue control and
token management are responsibilities of...
a) Network b) Session c) Application d) DataLink
ANSWER : b) Session Layer.
11) In OSI N/W Architecture, the routing is performed by
______
a) Network b) Session c) Application d) DataLink
Answer : Network Layer.
Networking
1) What is the difference between URL instance and
URLConnection instance?
ANSWER : A URL instance represents the location
of a resource, and a URLConnection instance represents a link for accessing or
communicating with the resource at the location.
2) How do I make a connection to URL?
ANSWER : You obtain a URL instance and then
invoke openConnection on it.
URLConnection is an abstract class, which means you can't
directly create instances of it using a constructor. We have to invoke
openConnection method on a URL instance, to get the right kind of connection
for your URL.
Eg. URL url;
URLConnection connection;
try{ url = new URL("...");
conection = url.openConnection();
}catch (MalFormedURLException e) { }
3) What Is a Socket?
A socket is one end-point of a two-way communication link
between two programs running on the network. A socket is bound to a port number
so that the TCP layer can identify the application that data is destined to be
sent.Socket classes are used to represent the connection between a client
program and a server program. The java.net package provides two classes--Socket
and ServerSocket--which implement the client side of the connection and the
server side of the connection, respectively.
4) What information is needed to create a TCP Socket?
ANSWER : The Local System’s IP Address and Port
Number. And the Remote System's IPAddress and Port Number.
5) What are the two important TCP Socket classes?
ANSWER : Socket and ServerSocket.
ServerSocket is used for normal two-way socket
communication. Socket class allows us to read and write through the sockets.
getInputStream() and getOutputStream() are the two methods available in Socket
class.
6) When MalformedURLException and UnknownHostException
throws?
ANSWER : When the specified URL is not connected
then the URL throw MalformedURLException and If InetAddress’ methods getByName
and getLocalHost are unabletoresolve the host name they throwan UnknownHostException.
Servlets
1) What is the servlet?
ANSWER : Servlets are modules that extend
request/response-oriented servers, such as Java-enabled web servers. For example,
a servlet might be responsible for taking data in an HTML order-entry form and
applying the business logic used to update a company's order database.
Servlets are to servers what applets are to browsers. Unlike
applets, however, servlets have no graphical user interface.
2) Whats the advantages using servlets than using CGI?
ANSWER : Servlets provide a way to generate
dynamic documents that is both easier to write and faster to run. Servlets also
address the problem of doing server-side programming with platform-specific
APIs: they are developed with the Java Servlet API, a standard Java extension.
3) What are the uses of Servlets?
ANSWER : A servlet can handle multiple requests
concurrently, and can synchronize requests. This allows servlets to support
systems such as on-line conferencing.
Servlets can forward requests to other servers and
servlets.Thus servlets can be used to balance load among several servers that
mirror the same content, and to partition a single logical service over several
servers, according to task type or organizational boundaries.
4) Which pakage provides interfaces and classes for
writing servlets?
ANSWER : javax
5) Whats the Servlet Interfcae?
ANSWER : The central abstraction in the Servlet
API is the Servlet interface. All servlets implement this interface, either
directly or, more commonly, by extending a class that implements it such as
HttpServlet.
Servlets-->Generic
Servlet-->HttpServlet-->MyServlet.
The Servlet interface declares, but does not implement,
methods that manage the servlet and its communications with clients. Servlet
writers provide some or all of these methods when developing a servlet.
6) When a servlet accepts a call from a client, it
receives two objects- What are they?
ANSWER : ServeltRequest: Which encapsulates the
communication from the client to the server. ServletResponse: Whcih
encapsulates the communication from the servlet back to the client.
ServletRequest and ServletResponse are interfaces defined by the javax.servlet
package.
7) What information that the ServletRequest interface
allows the servlet access to?
ANSWER : Information such as the names of the
parameters passed in by the client, the protocol (scheme) being used by the
client, and the names of the remote host that made the request and the server
that received it.
The input stream, ServletInputStream.Servlets use the input
stream to get data from clients that use application protocols such as the HTTP
POST and PUT methods.
8) What information that the ServletResponse interface
gives the servlet methods for replying to the client?
ANSWER : It Allows the servlet to set the
content length and MIME type of the reply.
Provides an output stream, ServletOutputStream and a Writer
through which the servlet can send the reply data.
9) What is the servlet Lifecycle?
ANSWER : Each servlet has the same life cycle:
A server loads and initializes the servlet (init())
The servlet handles zero or more client requests (service())
The server removes the servlet (destroy())
(some servers do this step only when they shut down)
10) How HTTP Servlet handles client requests?
ANSWER : An HTTP Servlet handles client requests
through its service method. The service method supports standard HTTP client
requests by dispatching each request to a method designed to handle that
request.
Java Fundamental Question and Answers
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