java多层组件内画图,该如何处理

import javax.imageio.*;import javax.swing.*;import java.awt.*;import java.awt.geom.*;import java.io.*;public class ImgP extends JFrame{    ImageCanvas ic;    final double culculateRatio(int width, int height){//计算缩放比例        double ratio;        if(getWidth()>=width && getHeight()>=height){            ratio = 1;            return ratio;        }        if((double)getWidth()/width > (double)getHeight()/height)            ratio = (double)getHeight() / height;        else ratio = (double)getWidth() / width;        return ratio;    }    public ImgP(){        Image image;        double ratio;        setSize(700, 500);        try {            image = ImageIO.read(new File("G:\\Image\\IMG_0783.jpg"));            ratio = culculateRatio(image.getWidth(null),image.getHeight(null));            ic = new ImageCanvas(ratio);            ic.setImage(image);           //如果将add(ic)一行替换成以下代码，画图有误           //JPanel panel = new JPanel();            //panel.add(ic);           //add(panel);            add(ic);            ic.concateZoom(ratio);        } catch (IOException ex) {        }    }        public static void main(String[] args) {        ImgP ip = new ImgP();        ip.setVisible(true);        ip.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    }}    class ImageCanvas extends JComponent{        Image img;        double ratio;        AffineTransform af = AffineTransform.getScaleInstance(1,1);        public ImageCanvas(double ratio){            this.ratio = ratio;        }        void setImage(Image m){            img = m;            paintImmediately(getBounds());            //concateZoom(0.3);        }        void concateZoom(double scale){            if (img==null)return;            af.preConcatenate(AffineTransform.getScaleInstance(scale,scale));            paintImmediately(getBounds());        }        @Override        protected void paintComponent(Graphics g) {            super.paintComponent(g);            if (img==null) {                g.setColor(Color.BLACK);                g.fillRect(0,0,getWidth(),getHeight());            }            else {                Graphics2D g2d = (Graphics2D)g;                g2d.setTransform(af);                g2d.drawImage(img, (int)(((getWidth()-img.getWidth(null)*ratio)/2)/ratio),                        (int)(((getHeight()-img.getHeight(null)*ratio)/2)/ratio), this);            }        }    @Override    public Dimension getPreferredSize() {return new Dimension(600, 400);}    }