一.簡單工廠模式

//介面
package Factory;

public interface Fruit {
    public void eat(); //吃
}

//實現介面類
package Factory;

public class Apple implements Fruit{

    public Apple() {
        // TODO Auto-generated constructor stub
    }

    public void eat() {
        // TODO Auto-generated method stub
        System.out.println("吃蘋果！"
 
);
    }

}
package Factory;

public class Banana implements Fruit{

    public Banana() {
        // TODO Auto-generated constructor stub
    }

    public void eat() {
        // TODO Auto-generated method stub
        System.out.println("吃香蕉！");
    }

}

package Factory;

public class Orange implements
 
 Fruit{

    public Orange() {
        // TODO Auto-generated constructor stub
    }

    public void eat() {
        // TODO Auto-generated method stub
        System.out.println("吃橘子");
    }

}

//工廠類
package Factory;

public class Factory {

    public Factory() {
        // TODO Auto-generated constructor stub
 


    }
    public static Fruit getInstance(String className){
        if("apple".equals(className))
            return new Apple(); //返回一個物件
        if("banana".equals(className))
            return new Banana();
        if("orange".equals(className))
            return new Orange();
        return null;
    }

}

//主方法
package Factory;

import java.util.Scanner;

public class FactoryTest {

    public FactoryTest() {
        // TODO Auto-generated constructor stub
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner scanner=new Scanner(System.in);
        String className=scanner.nextLine();//輸入想要建立物件的名字
       Fruit f=Factory.getInstance( className); //呼叫並接收
      f.eat();
    }

}

執行結果：


這個工廠類是最簡單的工廠類，可以體會到工廠模式的設計思想，但是每次想新增一個類都需要更改大量的程式碼，所以後來演變了一個更方便使用的工廠模式，利用反射機制建立物件，從而減少對程式碼的修改。

如果想再新增一個葡萄類
package Factory;

public class Grape implements Fruit{

public Grape() {
    // TODO Auto-generated constructor stub
}

@Override
public void eat() {
    // TODO Auto-generated method stub
    System.out.println("吃葡萄！");
}

}

//要在返回物件那多加一個建立葡萄類

package Factory;

public class Factory {

    public Factory() {
        // TODO Auto-generated constructor stub

    }
    public static Fruit getInstance(String className){
        if("apple".equals(className))
            return new Apple();
        if("banana".equals(className))
            return new Banana();
        if("orange".equals(className))
            return new Orange();
        if("grape".equals(className))
            return new Grape(); //這裡還要修改
        return null;
    }

}

執行結果：

這樣對程式碼的修改量會增大，這只是一個簡單的工廠模式，若果放到一個專案當中那修改的程式碼量遠遠比這個要多很多。

二.反射之工廠模式

//介面
package fanshe;

public interface Fruit {
    public void eat(); //吃

}

//實現介面的類
package fanshe;

public class Apple implements Fruit {

    public Apple() {
        // TODO Auto-generated constructor stub
    }

    public void eat() {
        // TODO Auto-generated method stub
        System.out.println("吃蘋果~！");
    }

}

package fanshe;

public class Banana implements Fruit{

    public Banana() {
        // TODO Auto-generated constructor stub
    }

    public void eat() {
        // TODO Auto-generated method stub
        System.out.println("吃香蕉~！");
    }

}

package fanshe;

public class Orange implements Fruit {

    public Orange() {
        // TODO Auto-generated constructor stub
    }

    public void eat() {
        // TODO Auto-generated method stub
        System.out.println("吃橘子~！");
    }

}

//工廠類
package fanshe;

public class Factory {

    public Factory() {
        // TODO Auto-generated constructor stub
    }
    public static Fruit getInstance(String className)
    {
        /*if("orange".equals(className))
            return new Orange();
        return null;*/
        Fruit fruit=null;
        try {
            fruit=(Fruit) Class.forName(className).newInstance();//建立物件


        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return fruit;   

    }

}

//主方法
package fanshe;

import java.util.Scanner;

public class FactortDemo {

    public FactortDemo() {
        // TODO Auto-generated constructor stub
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner scanner=new Scanner(System.in);
        String className=scanner.nextLine(); //輸入想要建立類的名字
     Fruit fruit=Factory.getInstance("fanshe."+className);
     fruit.eat();
    }

}

執行結果：

如果再想新增一個葡萄類直接新增類就可以了，不用再修改其他程式碼，減少了程式碼的修改量

package fanshe;

public class Grape implements Fruit{

    public Grape() {
        // TODO Auto-generated constructor stub
    }

    @Override
    public void eat() {
        // TODO Auto-generated method stub
        System.out.println("吃葡萄~！");
    }

}

執行結果：