Java設(shè)計(jì)模式之監(jiān)聽(tīng)器模式實(shí)例詳解

更新時(shí)間：2018年02月18日 10:06:50 作者：Jenkov

這篇文章主要介紹了Java設(shè)計(jì)模式之監(jiān)聽(tīng)器模式,結(jié)合實(shí)例形式較為詳細(xì)的分析了java設(shè)計(jì)模式中監(jiān)聽(tīng)器模式的概念、原理及相關(guān)實(shí)現(xiàn)與使用技巧,需要的朋友可以參考下

本文實(shí)例講述了Java設(shè)計(jì)模式之監(jiān)聽(tīng)器模式。分享給大家供大家參考，具體如下：

監(jiān)聽(tīng)器模式有三個(gè)要素——事件源、事件對(duì)象、監(jiān)聽(tīng)器。

事件源：顧名思義，事件發(fā)生的源頭，比如點(diǎn)擊的按鈕，屬于被監(jiān)聽(tīng)的對(duì)象；
事件對(duì)象：這個(gè)經(jīng)常和事件源混淆，它經(jīng)常被用來(lái)包裝事件源，切記，它畢竟是個(gè)事件，比如點(diǎn)擊事件，和事件源的區(qū)別自己感受，木有栗子；
監(jiān)聽(tīng)器：這個(gè)是監(jiān)聽(tīng)器模式的核心，定義事件發(fā)生后的動(dòng)作，通常事件對(duì)象作為監(jiān)聽(tīng)器中定義的函數(shù)入?yún)ⅰ?/p>

下面舉個(gè)簡(jiǎn)單的栗子：

故事背景是，小明是個(gè)不講衛(wèi)生的孩子，他媽媽很擔(dān)心他的健康，規(guī)定必須飯前洗手。

定義一個(gè)熊孩子。熊孩子就是被監(jiān)聽(tīng)的對(duì)象，是事件源，一切事件都是事件源發(fā)出，這似乎是句廢話。

public class Child {
  private String name;
  private RemindListener remindListener;
  public Child(String name){
    this.name = name;
  }
  public void eat() {
    if(null!=remindListener){
      remindListener.remind(new RemindWashingHandsEvent(this));
    }
    System.out.println("Child eat...");
  }
  public void addListener(RemindListener listener){
    remindListener = listener;
  }
}

接下來(lái)是看看事件對(duì)象，事件對(duì)象正如上面所述，包裝了事件源。我們?cè)谶@里定義一個(gè)飯前洗手事件。

public class RemindWashingHandsEvent {
  private Child child;
  public RemindWashingHandsEvent(Child child){
    this.child = child;
  }
}

事件對(duì)象定義了事件的屬性、狀態(tài)。
緊接著是定義事件發(fā)生后，監(jiān)聽(tīng)器的動(dòng)作，在這里是提醒洗手。

public class RemindListener {
  public void remind(RemindWashingHandsEvent remindWashingHandsEvent){
    System.out.println("listen to mom, washing hands before eating...");
  }
}

注意，監(jiān)聽(tīng)器主要封裝了動(dòng)作，僅此而已。

以上代碼，只是為了說(shuō)明監(jiān)聽(tīng)器模式原理，代碼通俗，不太優(yōu)雅。

下面繼承或?qū)崿F(xiàn)java標(biāo)準(zhǔn)庫(kù)，又隨手寫了一對(duì)代碼，夜深了，有時(shí)間再解釋。

public class Kid{
  private String name;
  private List<Listener> liteners;
  public Kid(String name) {
    this.name = name;
    this.liteners = Lists.newArrayList();
  }
  public void eat(){
    for(Listener listener:liteners){
      if(listener instanceof WashingHandsListener){
        WashingHandsListener washingHandsListener = (WashingHandsListener) listener;
        washingHandsListener.fireAfterEventInvoked(new WashingHandsEvent(this,"洗手"));
      }
    }
    System.out.println("吃飯...");
  }
  public void addListener(Listener listener){
    liteners.add(listener);
  }
}
public class Event extends EventObject {
  /**
   * Constructs a prototypical Event.
   *
   * @param source The object on which the Event initially occurred.
   * @throws IllegalArgumentException if source is null.
   */
  public Event(Object source) {
    super(source);
  }
}
public class WashingHandsEvent extends Event{
  private String eventName;
  /**
   * Constructs a prototypical Event.
   *
   * @param source The object on which the Event initially occurred.
   * @throws IllegalArgumentException if source is null.
   */
  public WashingHandsEvent(Object source,String eventName) {
    super(source);
    this.eventName = eventName;
  }
  public String getEventName() {
    return eventName;
  }
  public void setEventName(String eventName) {
    this.eventName = eventName;
  }
}
public interface Listener extends java.util.EventListener{
  public void fireAfterEventInvoked(Event event);
}
public class WashingHandsListener implements Listener{
  @Override
  public void fireAfterEventInvoked(Event event) {
    WashingHandsEvent washingHandsEvent = (WashingHandsEvent) event;
    System.out.println("飯前準(zhǔn)備"+ washingHandsEvent.getEventName());
  }
}
public class Test {
  public static void main(String[] args) {
    Kid xiaoming = new Kid("xiaoming");
    xiaoming.addListener(new WashingHandsListener());
    xiaoming.eat();
  }
}

輸出結(jié)果：