刚接触Swing编程的读者可能对JPanel的了解并不多，常常不清楚如何在JPanel中显示图像，而网上的很多教程又是通过JLabel来作为BufferedImage实例显示组件的，这其实不是一种很好的方法，不值得推荐。在JPanel中显示BufferedImage对象实例时，值得推荐的做法应该是通过重载paintComponent()方法来实现图像的显示与及时刷新。这种方法的大致实现可以分为以下几步。

1）重载JPanel中的 paintComponent()方法。

2）获取Graphics2D图形引擎绘制对象，使用drawImage方法绘制图像，代码如下：

protected void paintComponent(Graphics g) {
    Graphics2D g2d = (Graphics2D) g;
    g2d.clearRect(0, 0, this.getWidth(),
                        this.getHeight());
    if(sourceImage != null)
    {
        g2d.drawImage(sourceImage, 0, 0,
            sourceImage.getWidth(),
            sourceImage.getHeight(), null);
        if(destImage != null)
        {
            g2d.drawImage(destImage,
                    sourceImage.getWidth() + 10 ,
                0, destImage.getWidth(),
                destImage.getHeight(), null);
        }
    }
}

3）使用repaint()方法及时绘制更新。

以上简单的三步即可实现BufferedImage对象实例在JPanel的现实与刷新。

根据上述方法实现了一个完整的可以显示与刷新BufferedImage对象实例的ImagePanel类，代码如下：

package com.book.chapter.three;

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;

import javax.swing.JPanel;

public class ImagePanel extends JPanel {

    private static final long serialVersionUID = 1L;
    private BufferedImage sourceImage;
    private BufferedImage destImage;
    public ImagePanel()
    {
        // do nothing
    }
    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;
        g2d.clearRect(0, 0, this.getWidth(),
                    this.getHeight());
        if(sourceImage != null)
        {
            g2d.drawImage(sourceImage, 0, 0,
            sourceImage.getWidth(),
            sourceImage.getHeight(), null);
            if(destImage != null)
            {
                g2d.drawImage(destImage,
                sourceImage.getWidth() + 10 ,
                0, destImage.getWidth(),
                destImage.getHeight(), null);
            }
        }
    }
    public BufferedImage getSourceImage() {
        return sourceImage;
    }
    public void setSourceImage(BufferedImage sourceImage) {
        this.sourceImage = sourceImage;
    }
    public BufferedImage getDestImage() {
        return destImage;
    }
    public void setDestImage(BufferedImage destImage) {
        this.destImage = destImage;
    }

}