Java Classes Interview Preparation Guide
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Java Classes frequently Asked Questions in various Java Classes related job Interviews by interviewer. Get preparation of Java Classes job interview questions

76 Java Classes Questions and Answers:

Table of Contents

Java Classes Interview Questions and Answers
Java Classes Interview Questions and Answers

1 :: A stack stores data using first-in, last-out ordering.
A) True
B) False

Yes it is true ... Stack works on the Startegy of First In First Out

2 :: The type of data returned by a method need not be compatible with the return type specified by the method
A) True
B) False

Explanation: The type of data returned by a method must be compatible with the return type specified by the method. For example, if the return type of some method is boolean, you could not return an integer

A) its False

The return type must be compatible

3 :: This can be used inside any method to refer to the current object
A) True
B) False

Answer is False and i got it wrong inspite of being correct!!

Explanation:

this cannot be used within a static method. It can be used only within non-static methods.So the question asks whether it can be used inside any method......

4 :: In System.out.println() explain it.My doubt, we call static method with Class name but here what is "out"?

Actually System is class define in java.lang package...

class System{ //Member variables... static PrintStream out;

.................................

//Member methods...

.................

}
so out is a static reference of PrintStream class,which is define in java.io package and println() is a method of PrintStream class...
So ultimately, we can call println() method of static out reference of System class.
Syste.out.println();

5 :: What is the difference between instantiation & initialization?

Instance ation will not allocate memory, just a instance will be created.

Initialization will actually allocate memory.

6 :: If the method does not return a value, its return type must be void
A) True
B) False

It's true. If a method is not returning any value then we must have to specify it's return type as void.void indicates that method is not returning any value.

9 :: Stacks are controlled through two operations traditionally called ___ and _____
A) Push and Pull
B) Push and Pop
C) Pop and Pull
D) Pop and Peep

Ans is :(B)push and pop

Push :Push is used to insert elements in the stack.

Pop : Pop is used to extract elements from the stack.

10 :: In Java it is possible to define two or more methods within the same class that share the same name, as long as their parameter declarations are different
A) True
B) False

Yes it is True ...

In Java we can have to or more classes with the same name but the parameter list should be Different ... This Concept is called

Method Overloading or Function Overloading

In C++ we have the same Concept too ..

12 :: Tell me is it ok to say interfaces, classes are of polymorphism(i.e we can use those for different purposes). if not then why?

Inorder to reduce memory space and accessing the class members without instanciate Object is the Interface which will contain only abstract methods

13 :: Explain why the StringBuffer and the wrapper classes defined as final?

By defining a class as final we are restricting the one of the main feature of OOP ie., INHERITANCE. But JavaSoft(SUN) has provided this restricting feature because Java Developers thought that some methods cannot be modified by the users. Eg. for those are the methods in String , StringBuffrer ,StringBuilder , all Wrapper classes. As String is a standard class those methods should be as they are as developed by Sun. The user can not be permitted to change the functionality of those methods. If your application needs this type of situation u can decalre your class as final.

The user can't implement the method toUppercase( ) in String class as that it can convert only some of the characters into Uppercase.

16 :: What is meant by OO paradigm?

OO paradigm = Object Oriented Paradigm.

This is the basic concept of Object Oriented Languages.It actually means we have to only work out with objects.Communications take place between classes with the help of objects

Ex:- Java,C++ ,But not C(Function Oriented)

17 :: How to load a class from a remote server?

How can classes are loaded from remote server? Don't worry.... please visit the hypelink and will get your ans.... http://java.sun.com/developer/JDCTechTips/2001/tt0227.html#dynamic

21 :: What are static methods?

Static methods dont need class objects to call them where as nonstatic methods needs class objects to call them

22 :: Explain can a abstract class have a constructor? When would the constructor in the abstract class be called?

constructor can not be created in an abstract class.even though we write the constructor, when the constructor will be called..?only if the object is created. but we cannot create an object of abstract class.even though we create object using indirect way, there also, we cannot call the constructor of the abstract class.finally, constructor for the abstract class cannot be called.

23 :: Java does not supports recursion
A) True
B) False

Answer is B) False. Java supports recursion.

24 :: In interfaces the methods just defined without implementation then what is the purpose of defining the methods?

As By giving the Methods(Declaring) in Interface , We are telling to must follow exactly the same Signature for the given Methods. This wil be used when we are writing RMI Applications . Because in this case we just give the Interface to the User, so that user will come to know the Signature of the Method and later he/she will call it.