java学习总结(抽象类)

抽象类常用作“适配器”，因为无论一个接口中定义了多少方法，子类都必须实现。

import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

public class Mouse implements MouseListener {

 @Override
 public void mouseClicked(MouseEvent e) {
  // TODO Auto-generated method stub
  
 }

 @Override
 public void mouseEntered(MouseEvent e) {
  // TODO Auto-generated method stub
  
 }

 @Override
 public void mouseExited(MouseEvent e) {
  // TODO Auto-generated method stub
  
 }

 @Override
 public void mousePressed(MouseEvent e) {
  // TODO Auto-generated method stub
  
 }

 @Override
 public void mouseReleased(MouseEvent e) {
  // TODO Auto-generated method stub
  
 }

}

 以上是用在类Mouse实现(继承)接口MouseListener(java.awt.event.MouseListener),在子类Mouse中必须重写以上所有方法。为此，Java的设计者提供了一个抽象类：java.awt.event.Adapter,这个类实现了所有鼠标监听器接口(MouseListener,MouseWheelListener,MouseMotionListener),只是这个类定义为抽象类(abstract)。如下是Java的设计者已经写好的：

public abstract class MouseAdapter implements MouseListener, MouseWheelListener, MouseMotionListener {
    /**
     * {@inheritDoc}
     */
    public void mouseClicked(MouseEvent e) {}

    /**
     * {@inheritDoc}
     */
    public void mousePressed(MouseEvent e) {}

    /**
     * {@inheritDoc}
     */
    public void mouseReleased(MouseEvent e) {}

    /**
     * {@inheritDoc}
     */
    public void mouseEntered(MouseEvent e) {}

    /**
     * {@inheritDoc}
     */
    public void mouseExited(MouseEvent e) {}

    /**
     * {@inheritDoc}
     * @since 1.6
     */
    public void mouseWheelMoved(MouseWheelEvent e){}

    /**
     * {@inheritDoc}
     * @since 1.6
     */
    public void mouseDragged(MouseEvent e){}

    /**
     * {@inheritDoc}
     * @since 1.6
     */
    public void mouseMoved(MouseEvent e){}
}

 这样我们就可以根据自己的需要，选择性地重写java.awt.event.MouseAdapter这个抽象类中的方法。