接口与工厂

Thinking in Java
第四版练习18 创建一个Cycle接口，及其Unicycle、Bicycle、Tricycle实现。对每种类型的Cycle都创建工厂，然后编写代码使用这些工厂。

package interfaces;

interface Cycle{
    int wheels();
}
interface CycleFactory{
    Cycle getCycle();
}

class Unicycle implements Cycle{
    public int wheels(){
        return 1;
    }
}

class UnicycleFactory implements CycleFactory{
    public Cycle getCycle(){
        return new  Unicycle();
    }
}

class Tricycle implements Cycle{
    public int wheels(){
        return 3;
    }
}

class TricycleFactory implements CycleFactory{
    public Cycle getCycle(){
        return new  Tricycle();
    }
}

class Bicycle implements Cycle{
    public int wheels(){
        return 2;
    }
}
class BicycleFactory implements CycleFactory{
    public Cycle getCycle(){
        return new  Bicycle();
    }
}

public class E18_CycleFactory {
    public static void CycleWheels(CycleFactory factory){
        Cycle cycle=factory.getCycle();
        System.out.println(cycle.wheels());
    }
    public static void main(String[] args){
        CycleWheels(new TricycleFactory());
        CycleWheels(new BicycleFactory());
        CycleWheels(new UnicycleFactory()); 
    }
}

练习19，使用工厂方法创建一个框架，可以执行抛硬币和掷骰子的功能。

package interfaces;

interface Tossing{
    boolean result();
}

interface TossingFactory{
    Tossing getTossing();
}

class CoinTossing implements Tossing{
    private int events;
    private static final int EVENTS=2;
    public boolean result(){
        System.out.println(events);
        return  ++events!=EVENTS;
    }
}
class CoinTossingFactory implements TossingFactory{
    public Tossing getTossing(){
        return new CoinTossing();
    }
}

class DiceTossing implements Tossing{
    private int events;
    private static final int EVENTS=6;
    public boolean result(){
        System.out.println(events);
        return ++events!=EVENTS;
    }
}
class DiceTossingFactory implements TossingFactory{
    public Tossing getTossing(){
        return new DiceTossing();
    }
}
public class E19_TossingFactory {
    public static void simulate(TossingFactory factory){
        Tossing t=factory.getTossing();
        while(t.result()){
            ;
        }
    }
    public static void main(String[] args){
        simulate(new CoinTossingFactory());
        simulate(new DiceTossingFactory());

    }

}

接口是实现多重继承的途径，而生成遵循某个接口的对象的典型方式是工厂方法设计模式。

通过工厂方式，代码将完全与接口的实现分离，这样就可以透明的将某个实现替换为另一种实现。