缺省適配模式為一個接口提供缺省實現，這樣子類型從這個缺省實現進行擴展時，就不必實現原有接口的所有方法了。
應用：
windowslistener借口定義如下：
public interface WindowListener extends EventListener{
public void windowActivated(WindowEvent e)；
public void windowClosed(WindowEvent e)；
public void windowClosing(WindowEvent e)；
public void windowDeactivated(WindowEvent e)；
public void windowDeiconified(WindowEvent e)；
public void windowIconified(WindowEvent e)；
public void windowOpened(WindowEvent e)；
}
要實現這個接口，我們就必須實現它所定義的所有方法，但是實際上，我們很少需要同時用到所有的方法，我們要的只是其中的兩三個。為了不使我們實現多余的方法，
jdk WindowListener提供了一個WindowListener的默認實現類WindowAdapter類，這是一個抽象類，
public abstract class WindowAdapter implements WindowListener{
public void windowActivated(WindowEvent e){}
public void windowClosed(WindowEvent e){}
public void windowClosing(WindowEvent e){}
public void windowDeactivated(WindowEvent e){}
public void windowDeiconified(WindowEvent e){}
public void windowIconified(WindowEvent e){}
public void windowOpened(WindowEvent e){}
}