Java Sub-Interfaces.

Java Sub-Interfaces

• An interface can extend another interface, just as a class can extend another class.
• Interface is allowed to extend as many interfaces as it wants.
  Sub Interface example:

  interface Pricing {
    public String getPrice();
    public String getDiscount();
    public String DECIMALPATTERN="#";
    public static String getFormatted(double value) {
      DecimalFormat formatter = new DecimalFormat(DECIMALPATTERN);
      return formatter.format(value);
    }
  }
  // Pricing is a sub interface of Reputation
  interface Reputation extends Pricing{
    public String getInfo();
  }
  class Car implements Reputation {
    private final double price, discount;
    private final List<String> reputations= new ArrayList<>();
    public void addReputation(String reputation) {
      reputations.add(reputation);
    }
    public Car(double price, double discount) {
      this.price = price;
      this.discount = discount;
    }
    @Override
    public String getInfo() {
      String returns ="";
      for (String ret : reputations) {
        returns +="\n"+ret;
      }
      return returns;   
    }
    @Override
    public String getPrice() {
      return "$ "+Pricing.getFormatted(price);
    }
    @Override
    public String getDiscount() {
      return Pricing.getFormatted(discount)+"%";
    }
  }
  public class CarReputationApp {
    public static void main(String[] args) {
      Car myCar = new Car(100000,15); // instantiated object of class car
      System.out.println("Ordinary car price is " + myCar.getPrice());
      System.out.println("You've got a car discount of " + myCar.getDiscount());
      myCar.addReputation("\tComfortable to drive");
      myCar.addReputation("\tAdditional winter wheels");
      myCar.addReputation("\t2016 modell");
      System.out.println("Car reputations:" + myCar.getInfo());
    }
  }
  

  The result of this is:

  Ordinary car price is $ 100000
  You've got a car discount of 15%
  Car reputations:
  	Comfortable to drive
  	Additional winter wheels
  	2016 modell

  You can download this example here (needed tools can be found in the right menu on this page).
• A class that implements Reputation must also implement methods of the sub interface Pricing.