Static methods inside interface:

  • From 1.8 version onwards in addition to default methods we can write static methods also inside interface to define utility functions.
  • Interface static methods by-default not available to the implementation classes hence by using implementation class reference we can't call interface static methods. We should call interface static methods by using interface name. 
Ex: 
1) interface Interf { 
2) public static void sum(int a, int b) { 
3) System.out.println("The Sum:"+(a+b)); 
4) } 
5) } 
6) class Test implements Interf { 
7) public static void main(String[] args) { 
8) Test t = new Test(); 
9) t.sum(10, 20); //CE 
10) Test.sum(10, 20); //CE 
11) Interf.sum(10, 20); 
12) } 
13) }
  • As interface static methods by default not available to the implementation class, overriding concept is not applicable.
  • Based on our requirement we can define exactly same method in the implementation class, it's valid but not overriding. 
Ex:1 
1) interface Interf { 
2) public static void m1() {} 
3) } 
4) class Test implements Interf { 
5) public static void m1() {} 
6) }
It's valid but not overriding 
Ex:2 
1) interface Interf { 
2) public static void m1() {} 
3) }
4) class Test implements Interf { 
5) public void m1() {} 
6) }
This's valid but not overriding 
Ex3: 
1) class P { 
2) private void m1() {} 
3) } 
4) class C extends P { 
5) public void m1() {} 
6) }
This's valid but not overriding
From 1.8 version onwards we can write main() method inside interface and hence we can run interface directly from the command prompt. 
Ex: 
1) interface Interf { 
2) public static void main(String[] args) { 
3) System.out.println("Interface Main Method"); 
4) } 
5) }
At the command prompt: 
javac Interf.Java
java Interf