java - 按下鼠标时如何绘制蓝色矩形？

Question

这是我的代码。我想在按下鼠标时绘制一个蓝色矩形。该矩形将以鼠标指针为中心。我对事件一窍不通，因此非常感谢您的帮助和解释。

import javax.swing.*; 
import java.awt.*; 
import java.awt.event.*;  

 class MouseDemo extends JPanel implements MouseListener {
     int x, y; // location of mouse
     int sx=25, sy=25; // size of shape 
     JFrame frame;

     void buildIt() {     
         frame = new JFrame("MouseDemo");
         frame.add( this );
         this.x = 150;
         this.y = 150;
         this.addMouseListener(this); 
         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         frame.setSize(300, 300);
         frame.setLocation(200, 200);
         frame.setVisible(true);
     }

     public void paintComponent(Graphics g) {
         super.paintComponent(g);
         g.setColor( Color.blue );
         g.fillRect(x - sx/2, y - sy/2, sx, sy);
     }    

     // the method from MouseListener we're interested in this time
     @Override
     public void mousePressed( MouseEvent e) {
         e.getX();
         e.getY();
     }   

     // the other four methods from MouseListener
     // we don't use them, but they have to be present
     @Override public void mouseReleased( MouseEvent e) { }
     @Override public void mouseClicked( MouseEvent e) { }
     @Override public void mouseEntered( MouseEvent e) { }
     @Override public void mouseExited( MouseEvent e) { }

     public static void main(String[] args) {
         new MouseDemo().buildIt(); 
     }
}  

Answer 1

将你的方法修改为:

 // the method from MouseListener we're interested in this time
 @Override
 public void mousePressed( MouseEvent e) {
     this.x = e.getX();
     this.y = e.getY();
     this.repaint();
 }

您的代码在默认点 (150, 150) 处绘制带有正方形的 Jpanel。随着编辑。您将默认值 (150, 150) 更改为您鼠标所在的坐标，然后告诉 JPanel 它应该重新绘制自己，这将调用 paintComponent 方法来绘制鼠标位置处的正方形。