观察者模式（Observer）参考博文（http://www.cnblogs.com/hnrainll/archive/2011/12/29/2305582.html）
基本概念:
观察者模式属于行为型模式，其意图是定义对象间的一种一对多的依赖关系，当一个对象的状态发生改变时，所有依赖于它的对象都得到通知并被自动更新。
package observer;
public interface Subject {
public void attach(Observer observer);
public void detach(Observer observer);
public void notice();
}
package observer;
public interface Observer {
public void update();
}
Teacher需要实现Subject接口：
package observer;
import java.util.Vector;
public class Teacher implements Subject {
private Vector students;
private String num;
public Teacher(){
num="";
students=new Vector();
}
public Vector getVector(){
return students;
}
public String getNum() {
return num;
}
public void setNum(String num) {
this.num = num;
notice();
}
public void attach(Observer observer) {
students.add(observer);
}
public void detach(Observer observer) {
students.remove(observer);
}
public void notice() {
for(int i=0;i<students.size();i++){
((Observer)students.get(i)).update();
}
}
}
Students需要实现Observer接口：
package observer;
public class Student implements Observer {
private String num;
private Teacher teacher;
private String name;
public Student(String name,Teacher teacher){
this.name=name;
this.teacher=teacher;
}
public void update() {
num=teacher.getNum();
}
public void show(){
System.out.println("name="+name+"\n"+"num="+num);
}
}
Client（客户端）代码测试：
package observer;
import java.util.Vector;
public class Client {
public static void main(String[] args) {
Teacher teacher=new Teacher();
Vector students=teacher.getVector();
for(int i=0;i<5;i++){
Student student=new Student("pokid"+i,teacher);
students.add(student);
teacher.attach(student);
}
teacher.setNum("2317321");
for(int i=0;i<5;i++){
((Student)students.get(i)).show();
}
}
}
测试结果：
原文：http://www.cnblogs.com/pokid/p/4953577.html