工厂方法 Factory Method

1.工厂方法

    定义一个用于创建对象的接口，让子类决定实例化哪一个类。
    工厂方法使一个类的实例化延迟到其子类。
    工厂方法把简单工厂的内部逻辑判断移到了客户端代码来进行。
    你想要加功能，本来是改工厂类的，现在是修改客户端！

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2.结构图

3.代码

package com.hlf.designPatterns.FactoryMethod;

/**
 * 学雷锋，做好事
 * Created by Administrator on 2016/8/24.
 */
public interface LeiFeng {
    //帮助老人过马路
    void helpWalk();

    //捐钱
    void giveMoney();

    //帮人洗衣服
    void helpWash();
}

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package com.hlf.designPatterns.FactoryMethod;

/**
 * 学习雷锋的志愿者们
 * Created by hlf on 2016/8/24.
 */
public class Volunteers implements LeiFeng{
    @Override
    public void helpWalk() {
        System.out.println("Volunteers help people walk");
    }

    @Override
    public void giveMoney() {
        System.out.println("Volunteers help people give money");
    }

    @Override
    public void helpWash() {
        System.out.println("Volunteers help people wash");
    }
}

---

package com.hlf.designPatterns.FactoryMethod;

/**
 * 学习雷锋的大学生
 * Created by hlf on 2016/8/24.
 */
public class CollegeStudent implements LeiFeng{
    @Override
    public void helpWalk() {
        System.out.println("CollegeStudent help people walk");
    }

    @Override
    public void giveMoney() {
        System.out.println("CollegeStudent help people give money");
    }

    @Override
    public void helpWash() {
        System.out.println("CollegeStudent help people wash");
    }
}

---

package com.hlf.designPatterns.FactoryMethod;

/**
 * 如果是静态工厂的话是这样做的
 * Created by hlf on 2016/8/24.
 */
public class StaticFactory {
    //志愿者
    public static LeiFeng getVolunteers(){
        return new Volunteers();
    }
    //大学生
    public static LeiFeng getCollegeStudent(){
        return new CollegeStudent();
    }
}

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这时如果我要加入一个学习雷锋的小学生的话有麻烦， 这时用到工厂方法的话。

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package com.hlf.designPatterns.FactoryMethod;

/**
 * 后来加入的学习雷锋的小学生
 * Created by hlf on 2016/8/24.
 */
public class Pupil implements LeiFeng{
    @Override
    public void helpWalk() {
        System.out.println("Pupil help people walk");
    }

    @Override
    public void giveMoney() {
        System.out.println("Pupil help people give money");
    }

    @Override
    public void helpWash() {
        System.out.println("Pupil help people wash");
    }
}

---

package com.hlf.designPatterns.FactoryMethod;

/**
 * 工厂方法，就是要把简单工厂类抽象出来
 *
 * Created by hlf on 2016/8/24.
 */
public interface LeiFengFactory {
    LeiFeng getHelper();
}

---

package com.hlf.designPatterns.FactoryMethod;

/**
 * 后来加入的只要再创建一个对应的工厂就行了
 * Created by hlf on 2016/8/24.
 */
public class PupilFactory implements LeiFengFactory{
    @Override
    public LeiFeng getHelper() {
        return new Pupil();
    }
}

---

package com.hlf.designPatterns.FactoryMethod;

/**
 * 大学生工厂
 * Created by hlf on 2016/8/24.
 */
public class CollegeStudentFactory implements LeiFengFactory{
    @Override
    public LeiFeng getHelper() {
        return new CollegeStudent();
    }
}

---

package com.hlf.designPatterns.FactoryMethod;

/**
 * 志愿者工厂
 * Created by hlf on 2016/8/24.
 */
public class VolunteersFactory implements LeiFengFactory{
    @Override
    public LeiFeng getHelper() {
        return new Volunteers();
    }
}

---

package com.hlf.designPatterns.FactoryMethod;

/**
 * Created by hlf on 2016/8/24.
 */
public class TestFactoryMethod {
    public static void main(String[] args) {
        //如果用静态工厂方法创建
        LeiFeng collegeStudent = StaticFactory.getCollegeStudent();
        collegeStudent.giveMoney();
        collegeStudent.helpWalk();

        //如果想再加一个学习雷锋的对象小学生pupil的话，就要修改StaticFactory
        //这时用工厂方法就好点
        PupilFactory pupilFactory = new PupilFactory();
        LeiFeng pulil = pupilFactory.getHelper();
        pulil.giveMoney();
        pulil.helpWalk();
        pulil.helpWash();
    }
}

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结果

CollegeStudent help people give money
CollegeStudent help people walk

Pupil help people give money
Pupil help people walk
Pupil help people wash