package com.interview.design.pattern.behavioral;
import java.util.ArrayList;
import java.util.List;
/**
* Created_By: stefanie
* Date: 14-12-3
* Time: 下午2:56
*
* Observer pattern is used when there is one to many relationship between objects.
* such as if one object is modified, the objects depended on it are to be notified automatically.
*
* 当一个对象变化时，其它依赖该对象的对象都会收到通知，并且随着变化！对象之间是一种一对多的关系
* 类似Event Handler
*/
public class ObserverPattern {
static abstract class Observer {
protected Subject subject;
public abstract void update();
}
static class Subject {
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();
}
}
}
static class BinaryObserver extends Observer{
public BinaryObserver(Subject subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println( "Binary String: "
+ Integer.toBinaryString( subject.getState() ) );
}
}
static class OctalObserver extends Observer{
public OctalObserver(Subject subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println( "Octal String: "
+ Integer.toOctalString( subject.getState() ) );
}
}
static class HexaObserver extends Observer{
public HexaObserver(Subject subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println( "Hex String: "
+ Integer.toHexString( subject.getState() ).toUpperCase() );
}
}
public static void main(String[] args) {
Subject subject = new Subject();
new HexaObserver(subject);
new OctalObserver(subject);
new BinaryObserver(subject);
System.out.println("First state change: 15");
subject.setState(15);
System.out.println("Second state change: 10");
subject.setState(10);
}
}