Basic Core Java Interview Questions | Core java | Java Questions | Core Basics | Interview Questions | Java Questions | Core Java Basics | OOP in java | Object oriented programming | Object oriented programming in java

Basic Core Java Interview Questions | Core java | Java Questions | Core Basics | Interview Questions | Java Questions | Core Java Basics | OOP in java | Object oriented programming | Object oriented programming in java

1. What is OOP?

A. OOP extends for Object oriented programming. It is a paradigm of programming which works on object. In object oriented programming everything is in the form of          object. In java except primitives everything in the form of object. For converting primitives to object we can use wrapper classes concept in java.

2. What is Abstraction?

A. Abstraction is nothing but hiding the internal implementation and showing some set of services to the end user is called abstraction.

3. How can we use abstraction in java?

A. We can use abstraction in java with the help of Interface and Abstract class.

4. What is Abstract class?

A. Abstract class is special type of class which is declared by abstract keyword and used to achieve abstraction. It can't be instantiated(Object not created). It contains    

     abstract methods and non-abstract methods. We can define final block in abstract class. We can declare and define variables in abstract class. Abstract class also            contains constructors.    

5. What is interface?

A. Interface is a same as the java class but it is declared by interface keyword and it is used to achieve fully abstraction in java. We can not declare a variable in interface we have to define(provide a value to the variable) that variable. The variables which is define in interface are by default Public, Static and Final. It contains only Abstract methods upto java 7. It can't be instantiate. Interface does not contain constructors.

6. What is Inheritance?   

A. When child class aquire all the properties of perent class then it is called inheritance. It is also called IS-A relationship. For achiving inheritence throw class we use

     extends keyword. And inheritance concept is used for code reusability. 

7. What is static?

A. Static means one time initialisation. Static in java is keyword. We can use static keyword with block, variable, methods , inner classes. 

8.  What is super ?

A. Super is a keyword which is used to access parent  class property in java. 

9. Why we use this keyword in java?

A. this referce to current class propery so we use for accessing current class property.

10. Types of variables in java?

A. There are 3 types of variables in java.

    1) Local variable   2) Instance  variable   3) Class variable