java swing的背景图片按比例缩放

import java.awt.*;
import java.awt.image.BufferedImage;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class ScaleIcon implements Icon {

private BufferedImage i = null;
private Icon icon = null;

public ScaleIcon(Icon icon) {
this.icon = icon;
}

@Override
public int getIconHeight() {
return icon.getIconHeight();
}

@Override
public int getIconWidth() {
return icon.getIconWidth();
}

public void paintIcon(Component c, Graphics g, int x, int y) {
float wid = c.getWidth();
float hei = c.getHeight();
int iconWid = icon.getIconWidth();
int iconHei = icon.getIconHeight();

Graphics2D g2d = (Graphics2D) g;
g2d.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
g2d.scale(wid / iconWid, hei / iconHei);
icon.paintIcon(c, g2d, 0, 0);
}

public static void main(String[] args) {
ScaleIcon icon = new ScaleIcon(new ImageIcon(ClassLoader.getSystemResource("img/main.jpg")));
JLabel label = new JLabel(icon);
JFrame frame = new JFrame();
frame.getContentPane().add(label, BorderLayout.CENTER);
//                frame.getContentPane().add(new JButton("click"),BorderLayout.NORTH);
frame.setSize(800, 600);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}