享元模式

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

/**
 * 享元模式: 面向对象技术能够很好的解决一些灵活性或可扩展性问题, 可是在不少状况下须要在系统中增长类和对象的个数, 可是当这些彻底同样的对象数量太多的时候, 会致使运行的代价太高, 带来性能降低等问题.
 * 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, 相似于线程池, 数据库链接池, 他们均可以免不停的建立和销毁带来的高额代价. 享元模式是为了减小内存使用, 避免出现大量重复的建立和销毁对象的场景.
 * 享元模式的老是是共享细粒度独享, 将多个同一对象的访问集中起来, 没必要为每一个访问者建立一个单独的对象, 以此下降内存消耗.
 */
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，建立对象 ==> " + key);
            ITicket ticket = new TrainTicket(from, to);
            TicketFactory.sTicketPool.put(key, ticket);
            return ticket;
        }
    }
}