Java Interview questions and Answers?

Q: What is the difference between Abstract class and interface?

Ans:

Abstract Class	Interface
1) Abstract class can have abstract and non- abstract methods.	1) Interface can have only abstract methods.
2) It doesn't support Multiple Inheritance.	2) Interface Supports Multiple Inheritance
3) Abstract keyword is used to declare Abstract class	3) interface keyword is used to declare an interface.
4) Abstract class can contain static,non-static, final, non-final variables.	4) by default Interface variables are only static & final.
5) Abstract class can have static methods, main method.	5) Interface can't contain static method , main method.
6) Abstract class can contains Constructors	6) Interface can't contain Constructors.
7) Abstract class methods can be declared with public and non-public	7) By default all interface methods are public & abstract.
8) A abstract class can provide implement of interface.	8) A interface can't provide implementation of abstract class.
9) A abstract class can extends only one class.	9) A interface can extends any number of interfaces.
10) Object class is super class to all classes.	10) There is no super class for interface.
Ex: public abstract class B {       public abtract void fun1();       void fun2(); } public class A extends B {     public void fun1()     {            System.out.println("fun1 of class A is    calling");     }     public void fun2()    {         System.out.println("fun2 of class A is calling");     }    public static void main(String[] a)    {           A a1=new A();           a1.fun1();           a1.fun2();    } } O/P: fun1 of class A is calling fun2 of class A is calling	Ex: interface B {      int x=10;      void fun1(); } public class A  implements  B {      public void fun1()      {          System.out.println("fun1 of class A is calling");      }    public static void main(String[] a)   {          A a1=new A();          a1.fun1();    } } O/P: fun1 of class A is calling