Java Interface Statics.

Java Interface static methods and variables

• A static method is a method that is associated with the interface in which it is defined rather than with any object.
• Classes can NOT override static methods with their own implementation.
• An interface can contain constants which will be considered final and static,
• and which can be referred to directly
• through the interface name,
• and also appear in any class that implements the interface.
  Interface static method and variables example:

  interface Scaleable {
    // this will automatically be static final
    public String DECIMALPATTERN="#";
    // this will automaticly considered to be final
    public static enum Type {BIG, MEDIUM, SMALL};
    public void setScale(Type size);
    public String getArea();
    // This is a static method
    public static String getFormatted(double value) {
      DecimalFormat formatter = new DecimalFormat(DECIMALPATTERN);
      return formatter.format(value);
    }
  }
  class Rectangle implements Scaleable {
    private int width;
    private int height;
    @Override
    public void setScale(Type size) {
      switch (size) {
        case BIG:    width = 500; height = 500; break;
        case MEDIUM: width = 300; height = 300; break;
        case SMALL:  width = 200; height = 200; break;
      }
    }
    @Override
    public String getArea() {
      return Scaleable.getFormatted(width * height);
    }
  }
  class Circle implements Scaleable {
    private int radius;
    @Override
    public void setScale(Type size) {
      switch (size) {
        case BIG:    radius = 500;  break;
        case MEDIUM: radius = 300;  break;
        case SMALL:  radius = 200;  break;
      }
    }
    @Override
    public String getArea() {
      return Scaleable.getFormatted(radius * radius * Math.PI);
    }
  }
  
  public class interfaceStaticApp {
    public static void main(String[] args) {
      Rectangle rect = new Rectangle();
      rect.setScale(Scaleable.Type.BIG);
      System.out.println("Rectangle area = " + rect.getArea());
      Circle circle = new Circle();
      circle.setScale(Scaleable.Type.SMALL);
      System.out.println("Circle area = " + circle.getArea());
    }
  } 
  

  The result of this is:

  Rectangle area = 250000
  Circle area = 125664

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