java 接口与工厂

接口时实现多重继承的途径,而生产遵循某个接口的对象的典型方式就是工厂方法设计模式,这与直接调用构造器不同,我们在工厂对象上调用的是某种方法,而该工厂对象将生成接口的某个实现的对象,理论上通过这种方式,我们的代码将完全与接口的实现分离,这就使得我们可以透明地将某个实现替换为另一个实现

//如果不适应工厂模式,你的代码就必须在某处指定将要创建的service的确切类型,以便调用合适的构造器
//: interfaces/Factories.java
package object;
import static net.mindview.util.Print.*;

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

interface ServiceFactory {
  Service getService();
}

class Implementation1 implements Service {
  Implementation1() {} // Package access
  public void method1() {print("Implementation1 method1");}
  public void method2() {print("Implementation1 method2");}
}    

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

class Implementation2 implements Service {
  Implementation2() {} // Package access
  public void method1() {print("Implementation2 method1");}
  public void method2() {print("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 method1
Implementation1 method2
Implementation2 method1
Implementation2 method2
*///:~

使用工厂模式一个常见的原因是想要创建框架,假设正在创建一个对弈游戏系统,例如在棋盘上下国际象棋和西洋象棋

//如果Games 是一段复杂的代码,那么这种方式就允许你在不同类型的游戏中复用这段代码
//: interfaces/Games.java
// A Game framework using Factory Methods.
package object;

import static net.mindview.util.Print.*;

interface Game { boolean move(); }
interface GameFactory { Game getGame(); }

class Checkers implements Game {
  private int moves = 0;
  private static final int MOVES = 3;
  public boolean move() {
    print("Checkers move " + moves);
    return ++moves != MOVES;
  }
}

class CheckersFactory implements GameFactory {
  public Game getGame() { return new Checkers(); }
}    

class Chess implements Game {
  private int moves = 0;
  private static final int MOVES = 4;
  public boolean move() {
    print("Chess move " + moves);
    return ++moves != MOVES;
  }
}

class ChessFactory implements GameFactory {
  public Game getGame() { return new Chess(); }
}    

public class Games {
  public static void playGame(GameFactory factory) {
    Game s = factory.getGame();
    while(s.move())
      ;
  }
  public static void main(String[] args) {
    playGame(new CheckersFactory());
    playGame(new ChessFactory());
  }
} /* Output:
Checkers move 0
Checkers move 1
Checkers move 2
Chess move 0
Chess move 1
Chess move 2
Chess move 3
*///:~