corejava interviews 54

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.");

// Looks like a comment
The statement results in a compilation error
Looks like a comment
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?

It must have a package statement
It must be named Test.java
It must import java.lang
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

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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.

7) What is an array?

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?

String[ ] s;
String [ ]s:
String[ s]:
String s[ ]:
Ans : a, b and d

16) What is the value of a[3] as the result of the following array declaration?

1
2
3
4
Ans : d

17) Which of the following are primitive types?

byte
String
integer
Float
Ans : a.

18) What is the range of the char type?

0 to 2 16
0 to 2 15
0 to 2 16-1
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.

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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?

3
5
7
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"?

The double value 8.6
The string ""8.6"
The long value 8.
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

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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.

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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.

17) Casting occurs commonly between numeric types.

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?

Inner class
Anonymous classes
Method overloading
Method overriding
Ans : c

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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.

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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

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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
2
3
1 & 2
1,2 & 3
Ans : D