Java设计模式 - 观察者模式
观察者模式用于在一个对象被修改时通知其相关对象。
观察者模式是一种行为模式类别。
例子
import java.util.ArrayList;
import java.util.List;
class MyValue {
private List<Observer> observers
= new ArrayList<Observer>();
private int state;
public int getState() {
return state;
}
public void setState(int state) {
this.state = state;
notifyAllObservers();
}
public void attach(Observer observer){
observers.add(observer);
}
public void notifyAllObservers(){
for (Observer observer : observers) {
observer.update();
}
}
}
abstract class Observer {
protected MyValue subject;
public abstract void update();
}
class PrinterObserver extends Observer{
public PrinterObserver(MyValue subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println("Printer: " + subject.getState() );
}
}
class EmailObserver extends Observer{
public EmailObserver(MyValue subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println("Email: "+ subject.getState() );
}
}
class FileObserver extends Observer{
public FileObserver(MyValue subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println("File: " + subject.getState());
}
}
public class Main {
public static void main(String[] args) {
MyValue subject = new MyValue();
new FileObserver(subject);
new EmailObserver(subject);
new PrinterObserver(subject);
subject.setState(15);
subject.setState(10);
}
}
上面的代码生成以下结果。
File:15
Email:15
Printer:15
File:10
Email:10
Printer:10