设计模式之观察者模式

package com.test.lisener;

import java.util.ArrayList;
import java.util.List;

//An interface to be implemented by everyone interested in "Hello" events
interface HelloListener {
void someoneSaidHello();
}

//Someone who says "Hello"
class Initiater {
private List<HelloListener> listeners = new ArrayList<HelloListener>();

public void addListener(HelloListener toAdd) {
listeners.add(toAdd);
}

public void sayHello() {
System.out.println("Hello!!");

// Notify everybody that may be interested.
for (HelloListener hl : listeners)
hl.someoneSaidHello();
}
}

//Someone interested in "Hello" events
class Responder implements HelloListener {
@Override
public void someoneSaidHello() {
System.out.println("Hello there...");
}
}

class Responder2 implements HelloListener{

@Override
public void someoneSaidHello() {
System.out.println("hellll............");
}

}

class TestLisener {
public static void main(String[] args) {
Initiater initiater = new Initiater();
Responder responder = new Responder();
Responder2 responder2 = new Responder2();

initiater.addListener(responder);
initiater.addListener(responder2);

initiater.sayHello(); // Prints "Hello!!!" and "Hello there..."
}
}

输出

Hello!!
Hello there...
hellll............