OnJava8-Examples/interfaces/Factories.java

// interfaces/Factories.java
// <20>2016 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://mindviewinc.com/Books/OnJava/ for more book information.

interface Service {
  void method1();
  void method2();
}

interface ServiceFactory {
  Service getService();
}

class Implementation1 implements Service {
  Implementation1() {} // Package access
  public void method1() { System.out.println("Implementation1 method1"); }
  public void method2() { System.out.println("Implementation1 method2"); }
}

class Implementation1Factory implements ServiceFactory {
  @Override
  public Service getService() {
    return new Implementation1();
  }
}

class Implementation2 implements Service {
  Implementation2() {} // Package access
  public void method1() { System.out.println("Implementation2 method1"); }
  public void method2() { System.out.println("Implementation2 method2"); }
}

class Implementation2Factory implements ServiceFactory {
  @Override
  public Service getService() {
    return new Implementation2();
  }
}

public class Factories {
  public static void serviceConsumer(ServiceFactory fact) {
    Service s = fact.getService();
    s.method1();
    s.method2();
  }
  public static void main(String[] args) {
    serviceConsumer(new Implementation1Factory());
    // Implementations are completely interchangeable:
    serviceConsumer(new Implementation2Factory());
  }
}
/* Output:
Implementation1 method1
Implementation1 method2
Implementation2 method1
Implementation2 method2
*/