Java Interface.

Java Interface generally

• An interface can contain abstract method declarations, default methods, static methods and constant definitions.
• Interfaces is reference types and cannot be instantiated as we can do with classes.
  (the exception is when we are creating an anonymous inner class – see menu selection)
• It is up to the classes which are implementing the interface(s) to implement statements for the interface(s) methods.
• A number of common functionality can be imposed on a number of different classes this way:
  Interface example:

  interface Radio {
    boolean hasRadio();
  }
  class Car implements Radio {
    @Override
    public boolean hasRadio() { // Implemented method from the interface Radio:
      return true;
    }
  }
  class Cow implements Radio {
    @Override
    public boolean hasRadio() { // Implemented method from the interface Radio:
      return false;
    }
  }
  public class RadioApp {
    public static void main(String[] args) {
      Car myCar = new Car();
      Radio r = myCar;
      System.out.println(r.hasRadio());
      Cow myCow = new Cow();
      Radio c = myCow;
      System.out.println(c.hasRadio());
    }
  }
  

  The result of this is:

  true
  false

  You can download this example here (needed tools can be found in the right menu on this page).