适配器(adapter)
有的接口具有多个方法,比如WindowListener接口:
public interface WindowListener
{
void windowOpened(WindowEvent e);
void windowClosing(WindowEvent e);
void windowClosed(WindowEvent e);
void windowIconified(WindowEvent e);
void windowDeiconified(WindowEvent e);
void windowActivated(WindowEvent e);
void windowDeactivated(WindowEvent e);
}
实现一个接口就要实现其所有方法。如果只对接口中的一个方法感兴趣,可以对其他方法不做修改,但仍然要写出来加以实现,如:
class Terminator implements WindowListener
{
public void windowClosing(WindowEvent e)
{
if(user_agress)
System.exit(0);
}
public void windowOpened(WindowEvent e);
public void windowClosed(WindowEvent e);
public void windowIconified(WindowEvent e);
public void windowDeiconified(WindowEvent e);
public void windowActivated(WindowEvent e);
public void windowDeactivated(WindowEvent e);
}
这样书写很麻烦。
Java中定义了一些适配器(adapter)类,适配器类实现了相应接口中的所有方法,但方法内部没有做任何事情。可以通过扩展适配器类来实现接口,而不必实现接口中的所有方法,如:
class Terminator extends WindowAdapter
{
public void windowClosing(WindowEvent e)
{
if(user_agress)
System.exit(0);
}
}
进一步地,可以使用匿名内部类,如:
frame.addWindowListener(new
WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
if(user_agress)
System.exit(0);
}
});
上面代码实现一个匿名内部类,该匿名内部类扩展自WindowAdapter适配器。
参考
Cay S. Horstmann, Gary Cornell. JAVA核心技术卷I:基础知识(第八版).机械工业出版社.2011年4月第1版. 第8.1.5节.