享元模式

import java.util.Map;
import java.util.Random;
import java.util.concurrent.ConcurrentHashMap;

/**
 * 享元模式: 面向对象技术可以很好的解决一些灵活性或可扩展性问题, 但是在很多情况下需要在系统中增加类和对象的个数, 但是当这些完全一样的对象数量太多的时候, 会导致运行的代价过高, 带来性能下降等问题.
 * 享元模式正是为了该问题而诞生.
 * 享元模式是对象池的一种实现, 类似于线程池, 数据库连接池, 他们都可以避免不停的创建和销毁带来的高额代价. 享元模式是为了减少内存使用, 避免出现大量重复的创建和销毁对象的场景.
 * 享元模式的总是是共享细粒度独享, 将多个同一对象的访问集中起来, 不必为每个访问者创建一个单独的对象, 以此降低内存消耗.
 */
class Client {
	public static void main(String[] args) {
		ITicket ticket = TicketFactory.queryTicket("深圳北", "潮汕");
		ticket.showInfo("硬座");
		ticket = TicketFactory.queryTicket("深圳北", "潮汕");
		ticket.showInfo("软座");
		ticket = TicketFactory.queryTicket("深圳北", "潮汕");
		ticket.showInfo("硬卧");
	}
	interface ITicket {
		void showInfo(String bunk);
	}

	static class TrainTicket implements ITicket {
		private String from;
		private String to;
		private int price;

		public TrainTicket(String from, String to) {
			this.from = from;
			this.to = to;
		}

		@Override
		public void showInfo(String bunk) {
			this.price = new Random().nextInt(500);
			System.out.println(String.format("%s->%s：%s价格：%s 元", this.from, this.to, bunk, this.price));
		}
	}
	static class TicketFactory {
		private static Map<String, ITicket> sTicketPool = new ConcurrentHashMap<>();

		public static ITicket queryTicket(String from, String to) {
			String key = from + "->" + to;
			if (TicketFactory.sTicketPool.containsKey(key)) {
				System.out.println("使用缓存 ==> " + key);
				return TicketFactory.sTicketPool.get(key);
			}
			System.out.println("第一次查询，创建对象 ==> " + key);
			ITicket ticket = new TrainTicket(from, to);
			TicketFactory.sTicketPool.put(key, ticket);
			return ticket;
		}
	}
}