观察者模式最佳案例实现[JAVA]

/**
* American Stock Exchange market(ASE) has a list of stocks.A stock object has two perspective information,symbol and price.<br>
* Class <b>StockMarket</b> is a class that represents the stock market.<br>
* Its constructor generates a collection of stocks using random numbers to build 3-letter stock symbols and random numbers for initial stock price.<br>
* Implement a Java application when the stock price has been changed,all those investors who are interested in the stock market will be notified by receiving the most recent price.<br>
* Create a driver class to test your implementation.
*
*/

package com.v5ent.rapid4j.pattern;import java.util.ArrayList;import java.util.List;import java.util.Observable;import java.util.Observer;import java.util.Random;/** * American Stock Exchange market(ASE) has a list of stocks.A stock object has two perspective information,symbol and price.<br> * Class <b>StockMarket</b> is a class that represents the stock market.<br> * Its constructor generates a collection of stocks using random numbers to build 3-letter stock symbols and random numbers for initial stock price.<br> * Implement a Java application when the stock price has been changed,all those investors who are interested in the stock market will be notified by receiving the most recent price.<br> * Create a driver class to test your implementation. * @author Mignet * */public class StockTest {    public static void main(String[] args) {        StockMarket market = new StockMarket(10);        market.show();        market.invest();        market.shuffle();        market.show();    }}class StockMarket{    private List<Stock> list;    private int capacity;    public StockMarket(int capacity){        this.capacity=capacity;        init(this.capacity);    }    private  List<Stock> init(int n){        list= new ArrayList<Stock>();        for(int i=0;i<n;i++){            list.add(emitStock());        }        return list;    }    /**     * 股票看板     */    public void show(){        System.out.println("-------------Welcome to American Stock Exchange-------------------");        for(Stock s:list){s.show();}        System.out.println("------------------------------------------------------------------------");    }    /**     * 让投资人随机投资     */    public void invest(){        Investor inv1 = new Investor("巴菲特");        Investor inv2 = new Investor("索罗斯");        //让投资人随机投资        for(Stock s:list){            //比如巴菲特只投资价格是偶数的股票            if(Math.round(s.price)%2==0){                s.addObserver(inv1);                System.out.println(String.format("[%s]投资了[%s]:[%.2f]", inv1.name,s.symbol,s.price));            }            //比如索罗斯只投资价格是3的倍数的股票            if(Math.round(s.price)%3==0){                s.addObserver(inv2);                System.out.println(String.format("[%s]投资了[%s]:[%.2f]", inv2.name,s.symbol,s.price));            }        }    }    //生成随机股票    private Stock emitStock() {          StringBuilder val = new StringBuilder();  Stock s;        Random random = new Random();          for(int i = 0; i < 3; i++) {                  int temp =  65;  //or 97                val .append((char)(random.nextInt(26) + temp));          }        s = new Stock(val.toString(),random.nextFloat()*100);                  return s;    }          public void shuffle(){        for(Stock s:list){            s.shuffle();        }    }        class Stock extends Observable {        public Stock(String symbol, float price) {            this.symbol=symbol;            this.price=price;        }        public void show(){            System.out.println(String.format("[%s]:[%.2f]", this.symbol,this.price));        }        private String symbol;        private float price;        //价格随机波动        public void shuffle(){            this.price = this.price+new Random().nextInt(10)-5;            this.setChanged();            this.notifyObservers();        }    }    class Investor implements Observer{        public Investor(String name){            this.name = name;        }        private String name;        @Override        public void update(Observable o, Object arg) {            Stock s = (Stock)o;            System.out.println(String.format("[%s]获取到[%s]的最新价格[%.2f]",this.name, s.symbol,s.price));        }            }}