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);      }  }