在Java中如果要定义事件处理的方式，必须实作EventListener的子介面，例如实作 WindowListener来定义一些视窗事件的处理方式，WindowListener中定义了七个方法：
public interface WindowListener extends EventListener {
public void windowOpened(WindowEvent e);
public void windowClosing(WindowEvent e);
public void windowClosed(WindowEvent e);
public void windowIconified(WindowEvent e);
public void windowDeiconified(WindowEvent e);
public void windowActivated(WindowEvent e);
public void windowDecativated(WindowEvent e);
}
可以定义一个类别来实作这个介面，以完全想要的事件处理，例如：
public class WindowEventHandler implements WindowListener {
public void windowOpened(WindowEvent e) {}
public void windowClosing(WindowEvent e) {}
public void windowClosed(WindowEvent e) {
System.exit(0);
}
public void windowIconified(WindowEvent e) {}
public void windowDeiconified(WindowEvent e) {}
public void windowActivated(WindowEvent e) {}
public void windowDecativated(WindowEvent e) {}
}
然而这有个缺点，实作介面的原则是您必须实作当中所定义的所有方法，即使您对某些事件并不感兴趣，您也必须实作一个没有内容的空方法，代表您已经实作了介 面中定义的方法，然而有时，您并不知道介面中到底定义了几个方法，或是知道也不知道方法的确切名称与参数，即使您查了API，在程式中写下一堆没有实作内 容的方法也是很烦人的一件事。
WindowAdapter类别预先实作了WindowListener介面，每个方法中都是空的实作，如下所示：
public abstract class WindowAdapter
implements WindowListener {
public void windowOpened(WindowEvent e) {}
public void windowClosing(WindowEvent e) {}
public void windowClosed(WindowEvent e) {}
public void windowIconified(WindowEvent e) {}
public void windowDeiconified(WindowEvent e) {}
public void windowActivated(WindowEvent e) {}
public void windowDecativated(WindowEvent e) {}
}
可以继承WindowAdapter类别，并重新定义一些您所感兴趣的事件，如此一来，就可以避开之前所提及的，直接实作 WindowListener介面的缺点，如下所示：
public class WindowEventHandler extends WindowAdapter {
public void windowClosed(WindowEvent e) {
System.exit(0);
}
}
