Slide 11.8: Interfaces (cont.): An example

Interfaces (Cont.)

Why Interfaces?

It is used to achieve total abstraction.
Since Java does not support multiple inheritance in case of class, but by using interface it can achieve multiple inheritance.
It is also used to achieve loose coupling.
Interfaces are used to implement abstraction. So the question arises why use interfaces when we have abstract classes? The reason is, abstract classes may contain non-final variables, whereas variables in interface are final, public, and static.

An Interface Example

InterfaceDemo.java (interfaces)

// Demonstration of how interface works
// A simple interface 
interface in1 { 
  final int a = 10;             // public, static, and final 
  void display( String arg );   // public and abstract
}

// A class implements the interface. 
class InterfaceDemo implements in1 { 
  // Driver Code
  public static void main ( String[ ] args ) {
    InterfaceDemo i = new InterfaceDemo( );
    i.display( args[0] );
    System.out.print( " " + a );
  }
  // Implementing the capabilities of interface 
  public void display( String arg ) { System.out.print( arg ); } 
}

shell> java InterfaceDemo

Output: Result: