subject.java

来自「《Java与模式》一书的源代码」· Java 代码 · 共 37 行

package com.javapatterns.observer.variation;

import java.util.Enumeration;
import java.util.Vector;

public abstract class Subject
{
    private Vector observersVector = new java.util.Vector();

    public void attach(Observer observer)
    {
        observersVector.addElement(observer);
        System.out.println("Attached an observer.");
    }

    public void detach(Observer observer)
    {
        observersVector.removeElement(observer);
    }

    public void notifyObservers()
    {
        java.util.Enumeration enumeration = observers();
        while (enumeration.hasMoreElements())
        {
            System.out.println("Before notifying");
            ((Observer)enumeration.nextElement()).update();
        }
    }

    public Enumeration observers()
    {
        return ((java.util.Vector) observersVector.clone()).elements();
    }

}