解析Observer 模式

Observer模式主要通过observer的注册，当subject有什么变化时通过注册的observer,但是经典的设计中将add detach放在subject中，个人

觉得不是很好，因为注册和解绑和并不是和subject相关的行为，最好通过一个delegate将其放在一个class中来处理，因为找不到一个很好的例子

，找到某人以前的例子改写了一下。再次表示感谢。

public class HPStock extends Stock {


    public HPStock(String price, InvestorHandler handler) {
        super(price, handler);
        // TODO Auto-generated constructor stub
    }

    @Override
    protected void update() {
        System.out.println("hp current price is"+price);
        setChanged();
    }

}

public class IbmStock extends Stock {

	public IbmStock(String price, InvestorHandler handler) {
		super(price, handler);
	}

	@Override
	protected void update() {
		System.out.println("ibm stock current price is"+price);
		setChanged();
	}

}

public interface IInvestor {
    void update(String price);
}

public class InvestorHandler {
	private String price;
	
	public InvestorHandler(String price) {
		super();
		this.price = price;
	}

	private List<IInvestor> listInvestor = new ArrayList<IInvestor>();
	public void addInvestor(IInvestor aInvestor) {
		listInvestor.add(aInvestor);
	}

	public void removeInvestor(IInvestor aInvestor) {
		listInvestor.remove(aInvestor);
	}
	
	public void notifyObserver() {
		for (int index = 0; index < listInvestor.size(); index++) {
			IInvestor investor = listInvestor.get(index);
			investor.update(price);
		}
	}
}

public class Main {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		InvestorHandler handler = new InvestorHandler("90");
		Stock mstock = new IbmStock("90", handler);

		mstock.addInvestor(new WallSteetInvestor());
		mstock.addInvestor(new WallSteetInvestor());
		mstock.addInvestor(new ShanghaiInvestor());
		mstock.addInvestor(new ShanghaiInvestor());
		mstock.update();

		InvestorHandler handler1 = new InvestorHandler("30");
		Stock hpStock = new HPStock("30", handler1);
		hpStock.addInvestor(new WallSteetInvestor());
		hpStock.addInvestor(new WallSteetInvestor());
		hpStock.addInvestor(new ShanghaiInvestor());
		hpStock.addInvestor(new ShanghaiInvestor());
		hpStock.update();

	}

}

public class ShanghaiInvestor implements IInvestor {

	@Override
	public void update(String price) {
	  System.out.println("Shanghai investor current price is"+price);
	}

}

public abstract class Stock {

	protected String price;
	private InvestorHandler handler;

	public Stock(String price, InvestorHandler handler) {
		super();
		this.price = price;
		this.handler = handler;
	}

	protected abstract void update();
	public void addInvestor(IInvestor aInvestor) {
		handler.addInvestor(aInvestor);
	}

	public void removeInvestor(IInvestor aInvestor) {
		handler.removeInvestor(aInvestor);
	}

	protected void setChanged() {
		handler.notifyObserver();
	}
	
}

public class WallSteetInvestor implements IInvestor {

	@Override
	public void update(String price) {
	  System.out.println("wall steet current price is"+price);
	}

}