Java Listener继承 [英] Java Listener inheritance

问题描述

我有一个java类可以触发定制的java事件。代码的结构如下：

  public class AEvent extends EventObject {
 ... 
 } 
 
 public interface AListener extends EventListener {
 
 public void event1（AEvent event）; 
 
} 
 
 public class A {
 
 public synchronized void addAListener（AListener l）{
 .. 
} 
 
 public synchronized void removeAListener（AListener l）{
 .. 
} 
 
 protected void fireAlistenerEvent1（AEvent event）{
 .. 
} 
} 
  

一切正常，但我想创建一个A的新子类（称为B），这可能会触发一个新的事件。我正在考虑以下修改：

  public class BEvent extends AEvent {
 ... 
 
 
 public interface BListener extends AListener {
 
 public void event2（BEvent event）; 
} 
 
 public class B extends A {
 
 public synchronized void addBListener（BListener l）{
 .. 
} 
 
 public synchronized void removeBListener（BListener l）{
 .. 
} 
 
 protected void fireBListenerEvent2（AEvent event）{
 .. 
} 
 
} 
  

这是正确的方法吗？我正在网路上搜索示例，但找不到任何内容。

这个解决方案中有一些我不喜欢的东西：

1. BListener 有两种方法，一种使用 AEvent 其他用途 Bevent 作为参数。


2. B class都有 addAListener 和 addBListener 方法。我应该用private关键字隐藏addAListener吗？ [更新：无法隐藏私人关键字]


3. 与 fireAlistenerEvent1 和 fireBListenerEvent1 方法。

我使用的是Java版本1.5。

解决方案

我不明白为什么 BListener 应该扩展 AListener 。

你是否真的想强迫大家对 B 事件感兴趣实现 event1（）？

另外你不能添加 addAListener（） code>，因为派生类不能减少父类中存在的方法的可见性。此外，您不应该需要，否则您将违反 Liskov替代原则（每B必须可以做一个A可以做的事情）。

作为最后一句话，我会使 fire *（）方法受保护。通常没有理由保持公开，减少公共成员的数量使您的公共界面清洁。

I have a java class which fires custom java events. The structure of the code is the following:

public class AEvent extends EventObject {
...
}

public interface AListener extends EventListener {

  public void event1(AEvent event);

}

public class A {

  public synchronized void addAListener(AListener l) {
  ..
  }

  public synchronized void removeAListener(AListener l) {
  ..
  }

  protected void fireAListenerEvent1(AEvent event) {
  ..
  }
}

Everything works correctly, but I'd like to create a new subclass of A (call it B), which may fire a new event. I'm thinking of the following modification:

public class BEvent extends AEvent {
...
}

public interface BListener extends AListener {

  public void event2(BEvent event);
}

public class B extends A {

  public synchronized void addBListener(BListener l) {
  ..
  }

  public synchronized void removeBListener(BListener l) {
  ..
  }

  protected void fireBListenerEvent2(AEvent event) {
  ..
  }

}

Is this the correct approach? I was searching the web for examples, but couldn't find any.

There are a few things I don't like in this solution:

1. BListener has two methods one uses AEvent the other uses BEvent as a parameter.
2. B class both has addAListener and addBListener methods. Should I hide addAListener with private keyword? [UPDATE: it's not possible to hide with private keyword]
3. Similar problem with fireAListenerEvent1 and fireBListenerEvent1 methods.

I'm using Java version 1.5.

解决方案

I don't see a reason why BListener should extend AListener.

Do you really want to force everyone interested in B events to also implement event1()?

Also you can't add addAListener(), since a derived class can not reduce the visibility of a method that's present in the parent class. Also, you shouldn't need to, or you would violate the Liskov substitution principle (every B must be able to do everything an A can do).

And as a last remark, I'd make the fire*() methods protected. There's usually no reason at all to keep them public and reducing the number of public members keeps your public interface clean.

这篇关于Java Listener继承的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！