java组件显示不清晰

Question

我做了这个例子作为练习，这个程序在面板上显示鼠标的协调，它工作得很好，我一直收到的每个“paintComponent”例子的问题是，显示永远不会干净，刷新没有发生以下代码：

import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.Graphics;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class mousedrag extends JFrame {
   public mousedrag() {
      drag canvas = new drag("JAVA");
      add(canvas);
   }

   public static void main(String[] args) {
      mousedrag f = new mousedrag();
      f.setTitle("events");
      f.setSize(300, 200);
      f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      f.setLocationRelativeTo(null);
      f.setVisible(true);
   }

   static class drag extends JPanel {
      String name = "welcome to java";
      int x = 20, y = 20;

      public drag(String s) {
         this.name = s;
         addMouseMotionListener(new MouseMotionListener() {

            @Override
            public void mouseMoved(MouseEvent e) {
               x = e.getX();
               y = e.getY();
               repaint();
            }

            @Override
            public void mouseDragged(MouseEvent e) {    
            }
         });

      }

      @Override
      protected void paintComponent(Graphics g) {
         g.drawString(String.format("%03d %03d", x, y), x, y);
      }
   }
}

我的问题是：

Answer 1

你说：

the display is never clean the refresh isn't happening

原因是在paintComponent方法中没有调用super方法，因此组件永远无法执行其图像清理工作。要解决此问题，请通过更改以下内容调用super的方法：

@Override   
protected void paintComponent(Graphics g){
    g.drawString(String.format("%d %d", x,y), x, y);
}

到

@Override   
protected void paintComponent(Graphics g){
    super.paintComponent(g); // **********
    g.drawString(String.format("%d %d", x,y), x, y);
}