设计模式——观察者

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观察者类图：

以下程序模拟股票的状态更新功能（使用jdk对观察者支持，参考网上实现）
 
1.定义Observable 接口实现类，该类是设置股票的信息，并且在数据更新后会通知所有的观察者进行相关状态的更新。

package com.observer;
 
import java.util.Observable;
 
public class StockData extends Observable {
    private String symbol;
    private float close;
    private float high;
    private float low;
    private long volume;
 
    public StockData() {
    }
 
    public String getSymbol() {
        return symbol;
    }
 
    public float getClose() {
        return close;
    }
 
    public float getHigh() {
        return high;
    }
 
    public float getLow() {
        return low;
    }
 
    public long getVolume() {
        return volume;
    }
 
    public void sendStockData() {
        setChanged();
        notifyObservers();
    }
 
    public void setStockData(String symbol, float close, float high, float low,
            long volume) {
        this.symbol = symbol;
        this.close = close;
        this.high = high;
        this.low = low;
        this.volume = volume;
        sendStockData();
    }
}

package com.observer;
 
import java.text.DecimalFormat;
import java.text.DecimalFormatSymbols;
import java.util.Observable;
import java.util.Observer;
 
public class BigBuyer implements Observer {
    private String symbol;
    private float close;
    private float high;
    private float low;
    private long volume;
 
    public BigBuyer(Observable observable) {
        observable.addObserver(this); // 注册关系
    }
 
    public void update(Observable observable, Object args) {
        if (observable instanceof StockData) {
            StockData stockData = (StockData) observable;
            this.symbol = stockData.getSymbol();
            this.close = stockData.getClose();
            this.high = stockData.getHigh();
            this.low = stockData.getLow();
            this.volume = stockData.getVolume();
            display();
        }
    }
 
    public void display() {
        DecimalFormatSymbols dfs = new DecimalFormatSymbols();
        DecimalFormat volumeFormat = new DecimalFormat("###,###,###,###", dfs);
        DecimalFormat priceFormat = new DecimalFormat("###.00", dfs);
        System.out.println("Big Buyer reports... ");
        System.out.println("\tThe lastest stock quote for " + symbol + " is:");
        System.out.println("\t$" + priceFormat.format(close)
                + " per share (close).");
        System.out.println("\t$" + priceFormat.format(high)
                + " per share (high).");
        System.out.println("\t$" + priceFormat.format(low)
                + " per share (low).");
        System.out.println("\t" + volumeFormat.format(volume)
                + " shares traded.");
        System.out.println();
    }
}

package com.observer;
 
import java.text.DecimalFormat;
import java.text.DecimalFormatSymbols;
import java.util.Observable;
import java.util.Observer;
 
public class TradingFool implements Observer
{
private String symbol;
private float close;
 
public TradingFool(Observable observable)
    {
    observable.addObserver(this);//注册关系
    }
 
public void update(Observable observable,Object args)
    {
    if(observable instanceof StockData)
        {
        StockData stockData = (StockData)observable;
        this.symbol = stockData.getSymbol();
        this.close = stockData.getClose();
        display();
        }
    }
 
public void display()
    {
    DecimalFormatSymbols dfs = new DecimalFormatSymbols();
    DecimalFormat priceFormat = new DecimalFormat("###.00",dfs);
    System.out.println("Trading Fool says... ");
    System.out.println("\t" + symbol + " is currently trading at $" + priceFormat.format(close) + " per share.");
    System.out.println();
    }
}

package com.observer;
public class StockQuotes
{
public static void main(String[] args)
    {
    System.out.println();
    System.out.println("-- Stock Quote Application --");
    System.out.println();
 
    StockData stockData = new StockData();
 
    new TradingFool(stockData);
    new BigBuyer(stockData);
 
    stockData.setStockData("JUPM",16.10f,16.15f,15.34f,(long)481172);
    stockData.setStockData("SUNW",4.84f,4.90f,4.79f,(long)68870233);
    stockData.setStockData("MSFT",23.17f,23.37f,23.05f,(long)75091400);
    }
}

设计模式——观察者

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原文地址：http://blog.csdn.net/liuchangqing123/article/details/43938391