OnJava8-Examples/interfaces/Factories.java

// interfaces/Factories.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

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

interface ServiceFactory {
  Service getService();
}

class Service1 implements Service {
  Service1() {} // Package access
  @Override public void method1() {
    System.out.println("Service1 method1");
  }
  @Override public void method2() {
    System.out.println("Service1 method2");
  }
}

class Service1Factory implements ServiceFactory {
  @Override public Service getService() {
    return new Service1();
  }
}

class Service2 implements Service {
  Service2() {} // Package access
  @Override public void method1() {
    System.out.println("Service2 method1");
  }
  @Override public void method2() {
    System.out.println("Service2 method2");
  }
}

class Service2Factory implements ServiceFactory {
  @Override public Service getService() {
    return new Service2();
  }
}

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 Service1Factory());
    // Services are completely interchangeable:
    serviceConsumer(new Service2Factory());
  }
}
/* Output:
Service1 method1
Service1 method2
Service2 method1
Service2 method2
*/