Master the Prototype Pattern in Java: Clone Objects Efficiently

1. Initial Prototype Pattern

Copying homework is used as a metaphor for quickly reusing existing solutions, and the Prototype design pattern is introduced to model this concept in Java. Unlike the Flyweight pattern, which shares a single instance, the Prototype pattern creates copies of an existing object.

The Prototype pattern (Prototype Pattern) creates duplicate objects while preserving performance and belongs to the creational design patterns. It is useful when object creation is resource‑intensive or time‑consuming.

2. Diagram of Prototype Pattern

The diagram shows two prototype objects: XiaoQi (kind, gentle, versatile) and XiaoZi (generous, intellectual, filial). To avoid the time cost of finding such objects repeatedly, one can request an object "like XiaoQi" and obtain a copy.

When cloning, only height, weight, and hobbies (a reference type) are copied; the name is intentionally not duplicated.

3. Code Implementation

Base class Girl defines the fields and a cloneGirl method.

package prototype;

import java.util.List;

public class Girl {
    // name
    String name;
    // height cm
    int height;
    // weight kg
    int weight;
    // hobbies
    List<String> natures;
    // clone method
    public Girl cloneGirl(){
        // no initialization, returns null if not overridden
        return null;
    }
    @Override
    public String toString() {
        return "Girl{" +
                "name='" + name + '\'' +
                ", height=" + height +
                ", weight=" + weight +
                ", natures=" + natures +
                '}';
    }
}

Concrete prototype GirlLikeXiaoQi initializes XiaoQi’s attributes.

package prototype;

import java.util.ArrayList;
import java.util.Arrays;

public class GirlLikeXiaoQi extends Girl{
    public GirlLikeXiaoQi(){
        this.name = "小琪";
        this.height = 165;
        this.weight = 60;
        this.natures = Arrays.asList("善良","温柔","多才多艺");
    }
    @Override
    public Girl cloneGirl() {
        Girl girl = new Girl();
        // name not copied
        girl.height = this.height;
        girl.weight = this.weight;
        // deep copy of hobbies
        girl.natures = new ArrayList<>(this.natures);
        return girl;
    }
}

Concrete prototype GirlLikeXiaoZi initializes XiaoZi’s attributes.

package prototype;

import java.util.ArrayList;
import java.util.Arrays;

public class GirlLikeXiaoZi extends Girl{
    public GirlLikeXiaoZi(){
        this.name = "小紫";
        this.height = 175;
        this.weight = 70;
        this.natures = Arrays.asList("大方","知性","孝顺");
    }
    @Override
    public Girl cloneGirl() {
        Girl girl = new Girl();
        // name not copied
        girl.height = this.height;
        girl.weight = this.weight;
        girl.natures = new ArrayList<>(this.natures);
        return girl;
    }
}

Cache class stores prototype instances.

package prototype;

import java.util.HashMap;

public class GirlCache {
    static HashMap<String, Girl> girls;
    static {
        girls = new HashMap<>();
        girls.put("小琪", new GirlLikeXiaoQi());
        girls.put("小紫", new GirlLikeXiaoZi());
    }
    static Girl getGirl(String name){
        if(girls.containsKey(name)){
            return girls.get(name).cloneGirl();
        } else {
            return null;
        }
    }
}

Test class demonstrates usage.

package prototype;

public class Test {
    public static void main(String[] args) {
        // original XiaoQi
        Girl xiaoqi = GirlCache.girls.get("小琪");
        System.out.println(xiaoqi);
        // clone of XiaoQi
        Girl likeXiaoQi = GirlCache.getGirl("小琪");
        System.out.println(likeXiaoQi);
        // modify clone without affecting original
        likeXiaoQi.name = "小琪表妹";
        likeXiaoQi.natures.add("幽默");
        System.out.println(likeXiaoQi);
        System.out.println(xiaoqi);
        // request non‑existent prototype
        Girl likeyaya = GirlCache.girls.get("伢伢");
        System.out.println("小亮对象："+likeyaya);
        // clone XiaoZi and modify
        Girl likexiaozi = GirlCache.getGirl("小紫");
        likexiaozi.name = "紫棋";
        likexiaozi.natures.add("超喜欢唱歌");
        System.out.println("小明对象："+likexiaozi);
    }
}

4. Test Output

The program prints the original objects, their clones, and demonstrates that changes to a clone do not affect the cached prototype.

5. Conclusion

The Prototype pattern provides a convenient way to obtain objects that share the same state except for selected fields, much like copying homework; it enables efficient object creation without the overhead of building each instance from scratch.