java设计模式——享元模式

《大话设计模式》第二十六章

package ch26;

public class User {
	private String name;

	public User(String name) {
		this.name = name;
	}

	public String getName() {
		return name;
	}
}

 

package ch26;

public abstract class Website {
	public abstract void use(User user);
}

 

package ch26;

public class ConcreteWebsite extends Website {
	private String name;
	
	public ConcreteWebsite(String name) {
		this.name = name;
	}
	@Override
	public void use(User user) {
		System.out.println("网站分类:" + name + ",用户:" + user.getName());
	}

}

 

package ch26;

import java.util.HashMap;
import java.util.Map;

public class WebsiteFactory {
	private Map<String, Website> flyweights = new HashMap<String, Website>();
	
	public Website getWebsiteCategory(String key) {
		if (!flyweights.containsKey(key)) {
			flyweights.put(key, new ConcreteWebsite(key));
		}
		return flyweights.get(key);
	}
	
	public int getWebsiteCount() {
		return flyweights.size();
	}
}

 

package ch26;

/**
 * 享元模式
 * @author Administrator
 *
 */
public class Client {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		WebsiteFactory f = new WebsiteFactory();
		
		Website fx = f.getWebsiteCategory("产品展示");
		fx.use(new User("小菜"));
		
		Website fy = f.getWebsiteCategory("产品展示");
		fy.use(new User("大鸟"));
		
		Website fz = f.getWebsiteCategory("产品展示");
		fz.use(new User("娇娇"));
		
		Website fl = f.getWebsiteCategory("博客");
		fl.use(new User("老顽童"));
		
		Website fm = f.getWebsiteCategory("博客");
		fm.use(new User("桃谷六仙"));
		
		Website fn = f.getWebsiteCategory("博客");
		fn.use(new User("南海鳄神"));
		
		System.out.println("得到网站分类总数:" + f.getWebsiteCount());
	}

}

运行

网站分类:产品展示,用户:小菜
网站分类:产品展示,用户:大鸟
网站分类:产品展示,用户:娇娇
网站分类:博客,用户:老顽童
网站分类:博客,用户:桃谷六仙
网站分类:博客,用户:南海鳄神
得到网站分类总数:2

上面的关键代码是：

public Website getWebsiteCategory(String key) {
		if (!flyweights.containsKey(key)) {
			flyweights.put(key, new ConcreteWebsite(key));
		}
		return flyweights.get(key);
	}

JDK中的Integer.valueOf是经典例子，其代码如下：

public static Integer valueOf(int i) {
	final int offset = 128;
	if (i >= -128 && i <= 127) { // must cache 
	    return IntegerCache.cache[i + offset];
	}
        return new Integer(i);
    }