Swing, JFrame中加图片,图片放大缩小

import java.awt.Canvas;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;

import javax.swing.JButton;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;

public class ImageFrame extends javax.swing.JFrame {
private Canvas canvas;
private JButton smaller;
private JButton bigger;
private float scale=1f;
/**
* Auto-generated main method to display this JFrame
*/
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
ImageFrame inst = new ImageFrame();
inst.setLocationRelativeTo(null);
inst.setVisible(true);
}
});
}

public ImageFrame() {
super();
initGUI();<