Java OOPS Interview Questions

Concrete class is a class with implementation for all the methods in it. Concrete class defines all the abstract methods of an abstract class which it is extending. Object class is a concrete class.

concrete class is made up of 50% cement n 45% gravels mixed with !/2 glass of water....

The floating-point arithmetic in most computer languages is based on binary fractions (1/2, 1/4, 1/8, 1/16, ...) and not decimal fractions (1/10, 1/100, 1/1000, 1/1000,...)there is no ActionScript Number that is exactly equal to 0.1 because it require an infinite number of binary fractional bits.

Visual Studio uses partial classes to separate auto-generated code from user-generated code. Example:Let us consider that visual studio creates a file called Form1.Designer.cs which holds the designe...

Splitting the class into multiple files is called as partial class.The compiler treated the files as different classes but during compilation these files will be treated as a single class. Example:If...

First of all abstract is a key word. Abstract classes are having both defined methods and undefined methods. Concrete classes having only defined methods in the case of concrete classes the execution ...

Can any one give a real time example program for abstract class and virtual functions plzzzzzzzz

Compilation fails, why because it does not have proper syntax and structure.

This program gives error becoz here j=100 but the value of j is not used.

if condition is true then "hello" will print else "world".

iserrorpage is attribute of page, While executing the page it throws any errors then it returns Exception Object 

If in MyErrorPage.jsp<%@ page isErroPage="true" %>is written it doesn't mean this is an Error Object.If this page is included as error page in any other jsp (suppose MyPage.jsp) us...

this is so because it leads to a problem called "dirty diamond".
that is, say class B and C inherit from class A.
class B and C might override the methods in A.
Now if D inherits from B and C(multiple inheritance), there would be a problem that which overridden method would it inherit

Due to the naming complexity in Base & Drived classes,

We Can't provide a solution  every time using Inheritance with same name of member,methods.

That's why It's not allowed in JAVA.

Imp: Multiple Inheritance is allowed in Java In Only the case of Interfaces.

This is basically used to call the constructor of the base class. It is a method of course.

super is a keyword in Java because it is defined as keyword in java and super is not a keyword or variable which belongs to any class.

By creating object to an class by using  "new" keyword shows that JVM allocates memory in heap area.   

in heap

yes it can be done by singliton class

Preventing direct instantiationWe all know how objects are instantiated right? Maybe not everyone? Let's go through a quick refresher.Objects are instantiated by using the new keyword. The new keyword...

An abstract class can always have a constructor for a reason that an abstract class even though cannot be instantiated but it can be extended. Once its extended by its subclass. the object of the subc...

Class   Diagram  : They describe the static structure of a system.Package Diagram  : Package diagrams organize elements of a system into related groups to minimize depend...

Java is actually designed to work same as C++ but avoid complex features like operator overloading, friend functions, multiple inheritence.

In Java it is not possible to overloading OPERATOR such as +/-/* etc. We can do that is C++.
In Java there won't be any friend function. ...
That is why we can't use friend function overloading in Java

An Object is an physical entity of logical class definition, and in Java there is nothing called static object.

in java there is no concept of static object

call by value--->You are passing primitive value for your method argument.
call by ref--->You are passing object
call by address-->reference and address both are same.

In call by value, value is passed and in call by reference, base address is passed.

Run-time polymorphism provides the ability to use late-binding.  In other words, the function called or the data member accessed is not determined until run-time and is based on the type that a v...

Purpose of Runtime polymorphism:Run time polymorphism is a mechanism by which a call to overriden function is resolved at runtime rather than compile time.For e.gIf (user clicks link 1) then{obj1.over...

Defining a class within another class is known as nested class.

If class B is defined within class A, then B is known to A, but not outside of A.

Class B has access to the members, including private members of the Class A.

However,the class A does not have access to the members of Class B.

Logical grouping of classes—If a class is useful to only one other class, then it is logical to embed it in that class and keep the two together. Nesting such "helper classes" makes th...