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).
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