实例一：猫、狗与老鼠
假设猫是老鼠和狗的观察目标，老鼠和狗是观察者，猫叫老鼠跑，狗也跟着叫，使用观察者模式描述该过程。
类图：
代码：
import java.util.*;
public abstract class MySubject {
protected ArrayList observers = new ArrayList(); public abstract void attach(MyObserver obs); public abstract void detach(MyObserver obs); public abstract void cry(); }public class Cat extends MySubject
{
public void attach(MyObserver obs) { obs.add(obs); }
public void detach(MyObserver obs) { obs.remove(obs); }
public void cry() { for(Object obs:obs) { ((MyObserver)obs).response(); } }
}
public interface MyObserver {
public void response(); }
public class Mouse {
public void response() { //具体更新代码 } }
public class Dog {
public void response() { //具体更新代码 } }
实例二：自定义登录控件
Java事件处理模型中应用了观察者模式，下面通过一个实例来学习如何自定义Java控件，并给该控件增加相应的事件。该实例基于Java Swing/AWT控件，在Swing/AWT的相关类中封装了对事件的底层处理。
类图：
代码：
import javax.swing.*; import java.awt.event.*; import java.awt.*;
import java.util.EventObject; import java.util.EventListener;
public class LoginBean extends JPanel implements ActionListener { private LoginEventListener lel; private LoginEvent le; public LoginBean() { //详细代码 } public void addLoginEventListener(LoginEventListener lel) { this.lel=lel;
} private void fireLoginEvent(Object object,String userName,String password) { le=new LoginEvent(btnLogin,userName,password); lel.validateLogin(le); } public void actionPerformed(ActionEvent event) { if(btnLogin==event.getSource()) { String userName=this.txtUserName.getText(); String password=this.txtPassword.getText(); fireLoginEvent(btnLogin,userName,password); } if(btnClear==event.getSource()) { this.txtUserName.setText(\ this.txtPassword.setText(\ } } }
public class LoginEvent extends EventObject { private String userName; private String password; public LoginEvent(Object source,String userName,String password) { super(source); this.userName=userName; this.password=password; } public void setUserName(String userName) { this.userName=userName; } public String getUserName()
{ return this.userName; } public void setPassword(String password) { this.password=password; } public String getPassword() { return this.password; } }
public interface LoginEventListener extends EventListener { public void validateLogin(LoginEvent event); }
public class LoginValidatorA extends JFrame implements LoginEventListener { private LoginBean lb; public LoginValidatorA() { super(\ p=new JPanel(); this.getContentPane().add(p); lb=new LoginBean(); lb.addLoginEventListener(this); } public void validateLogin(LoginEvent event) { //详细代码 } }
public class LoginValidatorB extends JFrame implements LoginEventListener { private LoginBean lb; public LoginValidatorB() { super(\