繪製cricle

Question

我想要繪製具有後續特性的圓：

• 中心是其中用戶首先點擊鼠標的窗口上的點
• 半徑應之間的距離的長度第一次點擊鼠標並釋放時（即拖動鼠標）。

這裏就是我有這麼遠，但它沒有做什麼，我需要做的：

package assignment; 

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

import javax.swing.*; 

public class DrawCircle extends JFrame implements MouseListener 
{ 
    private int centerX; 
    private int centerY; 
    private int endPtX; 
    private int endPtY; 
    private double radius; 
    private double w; 
    private double h; 
    private CirclePanel circPanel; 

    /** constructor **/ 
    public DrawCircle() 
    { 
     this.setTitle("Click to Draw Circle"); 
     this.setSize(500, 500); 
     this.setPreferredSize(new Dimension(500, 500)); 
     this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     this.setVisible(true); 
     this.setResizable(false); 
     this.addMouseListener(this); 
     this.circPanel = new CirclePanel(); 
     this.circPanel.setPreferredSize(new Dimension(500, 500)); 
     this.add(this.circPanel); 
     pack(); 
    } 

    public void mousePressed(MouseEvent e) 
    { 
     centerX = e.getX(); 
     centerY = e.getY(); 
     circPanel.set(centerX, centerY, radius, radius); 
     repaint(); 
     pack(); 
    } 

    public void mouseReleased(MouseEvent e) 
    { 
     endPtX = e.getX(); 
     endPtY = e.getY(); 

     radius = Math.sqrt(Math.pow(endPtX - centerX, 2) + Math.pow(endPtY - centerY, 2)); 
    } 
    public void mouseEntered(MouseEvent e) {} 
    public void mouseExited(MouseEvent e) {} 
    public void mouseClicked(MouseEvent e){} 



    //circle panel 
    private class CirclePanel extends JComponent 
    { 
     private int x; 
     private int y; 
     private int w; 
     private int h; 

     public void set(int x, int y, double width, double height) 
     { 
      this.x = x; 
      this.y = y; 
      w = (int) width; 
      h = (int) height; 
     } 

     public void paintComponent(Graphics g) 
     { 
      g.drawOval(x, y, w, h); 
     } 
    } 

    //main method 
    public static void main (String [] args) 
    { 
     new DrawCircle(); 
    } 
} 

Answer 1

看起來你是在錯誤的地方，你不該做

circPanel.set(centerX, centerY, radius, radius); 
repaint(); 
pack(); 

在用戶放開鼠標之前不要繪製圓，因爲這是半徑設置的時候，並且在此之前半徑爲0，所以沒有繪製任何東西。嘗試將其移至mouseReleased方法。