优化JFrame重绘的方法：解决移动图形时屏幕频繁闪白的问题

问题原因 #

Swing 直接重写JFrame的paint方法时，默认重绘流程会先清空整个窗口背景，再绘制窗口边框、组件，最后才执行你写的图形绘制逻辑，背景清空的瞬间就会出现白屏闪烁。

可行解决方案 #

核心思路是用自带双缓冲的JPanel作为绘图容器，替换直接在JFrame上绘图的逻辑，双缓冲会先把所有图形绘制到后台缓冲区，绘制完成后一次性替换到屏幕上，完全消除闪烁。

修改步骤 #

1. 移除JFrame的paint重写逻辑，新增自定义DrawPanel类继承JPanel，所有绘图逻辑放在DrawPanel的paintComponent方法中
2. 将DrawPanel添加到JFrame的内容窗格，JPanel默认开启双缓冲，可显式声明加强兼容性
3. 优化冗余代码：Figure是引用类型，从数组取出修改属性后不需要再调用set放回数组，原对象已经被修改

修改后完整代码 #

figurestest/Figure.java（无变动）

package figurestest;
import java.awt.Graphics;

public abstract class Figure {
    public int x, y;
    public int w, h;

    public Figure (int x, int y, int w, int h) {
        this.x = x;
        this.y = y;
        this.w = w;
        this.h = h;
    }

    public abstract void paint (Graphics g);
    public abstract void mov (int dx, int dy);
}

figurestest/Rect.java（修正类名首字母大写，无逻辑变动，注意和文件名保持一致）

package figurestest;

import java.awt.*;

public class Rect extends Figure {

    public Rect (int x, int y, int w, int h) {
        super(x, y, w, h);
    }

    public void paint (Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        g2d.fillRect(this.x, this.y, this.w, this.h);
        g2d.drawRect(this.x,this.y, this.w,this.h);
    }

    public void mov (int dx, int dy){
        this.x += dx;
        this.y += dy;
    }
}

testapp.java（核心修改）

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.ArrayList;
import java.util.Random;

import figurestest.*;

class TestApp {
    public static void main (String[] args) {
        ListFrame frame = new ListFrame();
        frame.setVisible(true);
    }
}

// 自定义绘图面板
class DrawPanel extends JPanel {
    ArrayList<Figure> figs;
    public DrawPanel(ArrayList<Figure> figs) {
        this.figs = figs;
        // 显式开启双缓冲
        setDoubleBuffered(true);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // 所有图形绘制在这里执行
        for (Figure fig: figs) {
            fig.paint(g);
        }
    }
}

class ListFrame extends JFrame {
    ArrayList<Figure> figs = new ArrayList<Figure>();
    Random rand = new Random();
    DrawPanel drawPanel;

    ListFrame () {
        // 初始化绘图面板并添加到窗口
        drawPanel = new DrawPanel(figs);
        add(drawPanel, BorderLayout.CENTER);
        // 让面板获取焦点响应键盘事件
        drawPanel.setFocusable(true);
        drawPanel.requestFocus();

        this.addWindowListener (
            new WindowAdapter() {
                public void windowClosing (WindowEvent e) {
                    System.exit(0);
                }
            }
        );

        // 键盘事件绑定到绘图面板，避免焦点丢失
        drawPanel.addKeyListener (
            new KeyAdapter() {
                public void keyPressed (KeyEvent evt) {
                    Dimension size = drawPanel.getSize();
                    
                    int x = rand.nextInt(size.width);
                    int y = rand.nextInt(size.height);
                    int w = 5+ rand.nextInt(50);
                    int h = 5+ rand.nextInt(50);
                    if (evt.getKeyChar() == 'r') {
                        figs.add(new Rect(x,y, w,h));
                    } 
                    else if (evt.getKeyCode() == KeyEvent.VK_DOWN || evt.getKeyCode() == KeyEvent.VK_LEFT || evt.getKeyCode() == KeyEvent.VK_RIGHT || evt.getKeyCode() == KeyEvent.VK_UP ) {
                        if (figs.size() > 0){
                            int dx = 0;
                            int dy = 0;
                            if(evt.getKeyCode() == KeyEvent.VK_DOWN) dy = 2;
                            else if (evt.getKeyCode() == KeyEvent.VK_UP) dy = -2;
                            else if (evt.getKeyCode() == KeyEvent.VK_RIGHT) dx = 2;
                            else if (evt.getKeyCode() == KeyEvent.VK_LEFT) dx = -2;
                            
                            // 引用类型直接修改即可，不需要set回数组
                            Figure fig = figs.get(figs.size() -1);
                            fig.mov(dx,dy);
                        }
                    }
                    // 只重绘画板，不需要重绘整个窗口
                    drawPanel.repaint(); 
                }
            }
        );

        this.setTitle("Figures");
        this.setSize(350, 350);
    }
    // 移除原JFrame的paint重写
}

额外优化建议 #

如果后续图形数量较多还可以进一步优化：调用repaint(Rectangle bounds)只重绘图形变化的区域，不需要重绘整个面板，进一步提升流畅度。

内容的提问来源于stack exchange，提问作者Leonardo