30. Interface

• The only members of an interface are abstract methods
  (those with no data members, and with no non-abstract methods.)

• Interface has to be extended through inheritance.

• The descendent can be an interface, an abstract class, or a non-abstract class.

• Interface in Java:

  
      interface Container
      {
          public void put( Object  obj );
          public Object get();
  
      }//interface Container