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下面是一个典型的回调案例：公司员工工作，工作完成后主管要求员工汇报工作完成情况。
事件接口：
Java代码
package com.wxy.callback;
public interface Event {
/**
* 返回发生事件信息
* @return 事件信息
*/
public String happendEvent();
}
事件具体实现类：
Java代码
package com.wxy.callback;
public class EventA implements Event {
@Override
public String happendEvent() {
return "job has been finished!";
}
}
Java代码
package com.wxy.callback;
public class EventB implements Event {
@Override
public String happendEvent() {
return "job has been finished!";
}
}
主管类：
Java代码
package com.wxy.callback;
public class Boss {
private String name;
public Boss(String name) {
this.name = name;
}
public void getStaffEvent(Staff staff, Event event) {
System.out.println("the msg what the boss received is--" + staff.getName() + ":"
+ event.happendEvent());
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
员工类：
Java代码
package com.wxy.callback;
public class Staff {
private Event event; //事件
private String name; //员工姓名
private Boss boss; //员工所属主管
/**
* 员工构造器
* @param name 员工姓名
* @param boss 传入Boss对象，便于回调反馈工作状况
*/
public Staff(String name, Boss boss) {
this.name = name;
this.boss = boss;
}
public void doWork() {
System.out.println(name + " is doing working...");
//do somtething.....
for (int i = 0; i < 10; i++) {
System.out.println("sheep" + i);
}
System.out.println(name + " was finished work!");
//tell the boss what has happend,这里就是boss的回调方法
boss.getStaffEvent(this, event);
}
public Event getEvent() {
return event;
}
public void setEvent(Event event) {
this.event = event;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Boss getBoss() {
return boss;
}
public void setBoss(Boss boss) {
this.boss = boss;
}
}
测试类：
Java代码
package com.wxy.callback;
public class StaffBossTest {
public static void main(String args[]) {
//初始化员工和主管
Boss boss = new Boss("boss");
Staff staffA = new Staff("staffA", boss);
Staff staffB = new Staff("staffB", boss);
//主管发放了两个新任务
Event event1 = new EventA();
Event event2 = new EventB();
//员工接受任务开始干活
staffA.setEvent(event1);
staffB.setEvent(event2);
//员工干晚活，及时向主管反馈工作情况
staffA.doWork();
staffB.doWork();
}
}
测试结果：
Java代码
staffA was finished work!
the msg what the boss received is--staffA:job has been finished!
staffB is doing working...
sheep0
sheep1
sheep2
sheep3
sheep4
sheep5
sheep6
sheep7
sheep8
sheep9
staffB was finished work!
the msg what the boss received is--staffB:job has been finished!
可以看到，当员工完成工作时（即触发某事件时），staff对象调用boss对象的方法，实现回调功能。设计模式中，观察者模式也是一个典型的应用回调机制的例子。
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