Java Interface Defaults.

Java Interface and default methods

• Default methods in a interface is a common implementation for all classes that implements it.
• Classes can override default methods with their own implementation.
  Interface default method example:

  interface Radio {
    public boolean hasRadio();
    default public String containRadio() {
      return "The fact that the " + getClass().getSimpleName() + 
            " has a radio is " + hasRadio();
    }
  }
  class Cow implements Radio{
    @Override
    public boolean hasRadio() {
      return false;
    }
  }
  class Car implements Radio {
    @Override
    public boolean hasRadio() {
      return true;
    }
    @Override
    public String containRadio() {
      if (hasRadio()){return "This is a car that has a radio";}
      else {return "This is a car that has no radio";}
    }
  }
  public class InterfaceDefaultApp {
      public static void main(String[] args) {
      Radio carRadio=new Car();
      System.out.println(carRadio.containRadio());
      Radio cowRadio=new Cow();
      System.out.println(cowRadio.containRadio());
      }
  }
  

  The result of this is:

  This is a car that has a radio
  The fact that the Cow has a radio is false

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