MouseListener

import java.awt.*;
import java.awt.event.*;
import java.awt.event.MouseListener;
import java.util.EventListener;
import java.awt.event.MouseMotionListener;
public class DrawLineApp extends Frame implements MouseListener,MouseMotionListener{
   
   
   
    public static void main(String args[]){
        new DrawLineApp();
        }
   
    }


程序运行的结果，提示：

E:\Java\JCreator Pro\MyProjects\DrawLineApp\DrawLineApp.java:6: DrawLineApp 不是抽象的  ，并且未覆盖 java.awt.event.MouseListener中的抽象方法mouseExited(java.awt.event.MouseEvent)
public class DrawLineApp extends Frame implements MouseListener,MouseMotionListener{

为什么？

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