当创建给定类的实例的过程很昂贵或很复杂时，就使用原型模式。原型模式允许你通过复制现有的实例来创建新的实例。

示例—创建怪物

你设计的游戏中，需要怪兽的特征能够随着场景的变换而演化。例如在海底世界，创建海怪；在沙漠中，创建沙蝎怪物；在天空中，创建鸟人怪。由于创建怪物的过程比较复杂，需要在特定的类中统一复制创建，达到解耦的目的。

UML图表示

原型模式-创建怪物

代码演示

怪物抽象基类

package Prototype;

public abstract class Monster implements Cloneable {
    private String scene;
    private String name;
    Monster(String scene, String name){
        this.scene = scene;
        this.name = name;
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

    public String getScene() {
        return scene;
    }

    public void setScene(String scene) {
        this.scene = scene;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

海怪类

package Prototype;

public class SeaMonster extends Monster {
    SeaMonster(String scene, String name) {
        super(scene, name);
    }

    SeaMonster(String name) {
        super("sea", name);
    }
}

沙蝎类

package Prototype;

public class Scorpion extends Monster {
    Scorpion(String scene, String name) {
        super(scene, name);
    }

    Scorpion(String name){
        super("sand",name);
    }
}

鸟人类

package Prototype;

public class Birdy extends Monster {
    Birdy(String scene, String name) {
        super(scene, name);
    }

    Birdy(String name){
        super("sky",name);
    }
}

怪物注册类

package Prototype;

import java.util.HashMap;

public class MonsterRegistry {

    private HashMap<String, Monster> monsterDB ;

    MonsterRegistry(){
        monsterDB = new HashMap();
        monsterDB.put("sea", new SeaMonster("Sea Monster"));
        monsterDB.put("sand",new Scorpion("Sand Scorpion"));
        monsterDB.put("sky", new Birdy("Birdy"));
    }

    public Monster getMoster(String scene) throws CloneNotSupportedException {
        Monster correctMonster =  monsterDB.get(scene);
        return (Monster)correctMonster.clone();
    }
}

怪物生成类

package Prototype;

import java.util.Random;

public class MonsterMaker {

    private MonsterRegistry registry;
    private Random random = new Random(47);

    MonsterMaker(){
        registry = new MonsterRegistry();
    }

    void makeRandomMonster(String scene) throws CloneNotSupportedException {
        int count = random.nextInt(10);

        String name = "";

        for (int i = 0; i < count ; i++){
            Monster monster = registry.getMoster(scene);
            name = monster.getName();
        }

        System.out.println("You will fight with " + count + " " + name + " in " + scene + ". ");
    }
}

测试代码

package Prototype;

public class PrototypeDriver {
    public static void main(String[] args) throws CloneNotSupportedException {

        MonsterMaker monsterMake = new MonsterMaker();

        System.out.println("You're in sea. ");
        monsterMake.makeRandomMonster("sea");

        System.out.println("You're in sky. ");
        monsterMake.makeRandomMonster("sky");

        System.out.println("You're in sand. ");
        monsterMake.makeRandomMonster("sand");


    }
}

测试结果

You're in sea. 
You will fight with 8 Sea Monster in sea. 
You're in sky. 
You will fight with 5 Birdy in sky. 
You're in sand. 
You will fight with 3 Sand Scorpion in sand.