面向对象设计模式：创建型模式之原型模式

一、引入

二、代理模式，Prototype Pattern

代理模式实现了一个原型接口用于创建当前对象的克隆。

2.1 Intent 意图

• Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype. 使用原型实例指定要创建的对象类型，并通过克隆此原型来创建新对象

2.2 Applicability 适用性

• When a system should be independent of how its products are created, composed, and represented. 当一个系统应该独立于它的产品创建，构成和表示时
• When the classes to instantiate are specified at run-time, for example, by dynamic loading. 当要实例化的类是在运行时刻指定时，例如，通过动态装载.
• To avoid building a class hierarchy of factories that parallels the class hierarchy of products. 为了避免创建一个与产品类层次平行的工厂类层次时. (工厂模式介绍)
• When instances of a class can have one of only a few different combinations of state. 当一个类的实例只能有几个不同状态组合中的一种时.

2.3 类图

• Prototype: Declares an interface for cloning itself. 声明一个用于克隆自身的接口
• ConcretePrototype: Implements an operation for cloning itself. 实现一个克隆自身的操作

2.4 应用实例：使用下划线或消息框展示字符串

To show a string with underline or message box:

• Conventionally, we have to design three different classes to show a string with underline or message box
• However, we will design too many classes to show different underline or message box styles

---

• Prototype：

public interface Product extends Cloneable {public abstract void use(String s);public abstract Product createClone();
}

public class MessageBox implements Product {private char decochar;public MessageBox(char decochar) {this.decochar = decochar;}public void use(String s) {int length = s.getBytes().length;for (int i = 0; i < length + 4; i++) {System.out.print(decochar);}System.out.println("");System.out.println(decochar + " "  + s + " " + decochar);for (int i = 0; i < length + 4; i++) {System.out.print(decochar);}System.out.println("");}public Product clone() {Product p = null;try {p = (Product) super.clone();} catch (CloneNotSupportedException e) {e.printStackTrace();}return p;}
}

public class UnderlinePen implements Product {private char ulchar;public UnderlinePen(char ulchar) {this.ulchar = ulchar;}public void use(String s) {int length = s.getBytes().length;System.out.println("\""  + s + "\"");System.out.print(" ");for (int i = 0; i < length; i++) {System.out.print(ulchar);}System.out.println("");}public Product clone() {Product p = null;try {p = (Product) super.clone();} catch (CloneNotSupportedException e) {e.printStackTrace();}return p;}
}

• Manager：

public class Manager {private HashMap showcase = new HashMap<String, Product>();public void register(String name, Product proto) {showcase.put(name, proto);}public Product create(String protoname) {Product p = (Product) showcase.get(protoname);return p.clone();}
}

• ClientDemo

public class Main {public static void main(String[] args) {// 准备Manager manager = new Manager();UnderlinePen upen = new UnderlinePen('~');MessageBox mbox = new MessageBox('*');MessageBox sbox = new MessageBox('/');manager.register("strong message", upen);manager.register("warning box", mbox);manager.register("slash box", sbox);// 生成Product p1 = manager.create("strong message");p1.use("Hello, world.");Product p2 = manager.create("warning box");p2.use("Hello, world.");Product p3 = manager.create("slash box");p3.use("Hello, world.");}
}

2.4 应用实例：JDK java.lang.Object java.lang.Cloneable

java.lang.Object