Interface+工厂方法设计模式

package interfaces;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 {  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 {  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 method1Implementation1 method2Implementation2 method1Implementation2 method2*///:~

与直接调用构造方法不同，在工厂对象上调用的是creation方法，该工厂对象会生成接口的某种具体实现。如果不使用工厂方法，就必须在某处指出要创建的Service的确切类型，以便用合适的构造方法。

如果使用匿名内部类，会更简洁些。

interface Service {  void method1();  void method2();}interface ServiceFactory {  Service getService();}class Implementation1 implements Service {  private Implementation1() {}  public void method1() {System.out.println("Implementation1 method1");}  public void method2() {System.out.println("Implementation1 method2");}  public static ServiceFactory factory =    new ServiceFactory() {      public Service getService() {        return new Implementation1();      }    };}class Implementation2 implements Service {  private Implementation2() {}  public void method1() {System.out.println("Implementation2 method1");}  public void method2() {System.out.println("Implementation2 method2");}  public static ServiceFactory factory =    new ServiceFactory() {      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(Implementation1.factory);    // Implementations are completely interchangeable:    serviceConsumer(Implementation2.factory);  }} /* Output:Implementation1 method1Implementation1 method2Implementation2 method1Implementation2 method2*///:~