[code here]Need modification:Make my DrawPanel keep what I have paint

Question

Hi
please try it first
it's to draw some random shade on a JPanel
I just want the DrawPanel keep the random shades when resize.....
Thank you for your patience
DrawFrame.java
import javax.swing.*;
import java.awt.*;
public class DrawFrame extends JFrame {
  public static Shade[] shades;
  static {
    shades = new Shade[] {
        new CircleType(), new RectType(), new DiamondType()
  static InfoPanel ip = new InfoPanel();
  static DrawPanel dp = new DrawPanel();
  public DrawFrame() {
    JButton draw = new JButton("draw");
    Container cp = this.getContentPane();
    cp.add(new JLabel("Created by iooirrr on 2003.4.19~4.21 version 0.3"), BorderLayout.NORTH);
    JScrollPane dpjsp = new JScrollPane(dp);
    dpjsp.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
    dpjsp.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
    cp.add(dpjsp, BorderLayout.CENTER);
ScrollPaneLayout spl = new ScrollPaneLayout();
    JScrollPane ipjsp = new JScrollPane(ip);
    ipjsp.setLayout(spl);
    ipjsp.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
    ipjsp.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
    cp.add(ipjsp, BorderLayout.WEST);
String[] shadename = new String[shades.length];
    for (int i = 0; i < shades.length; i ++) {
      shadename[i] = shades.getName();
ip.shadeList.setListData(shadename);
Rectangle max = GraphicsEnvironment.getLocalGraphicsEnvironment().getMaximumWindowBounds();
this.setLocation(0, 0);
this.setSize(max.width, max.height);
this.show();
public void make(Container cp, Component c, GridBagLayout gbl, GridBagConstraints gbc) {
// gbc.fill = GridBagConstraints.BOTH;
gbl.setConstraints(c, gbc);
cp.add(new JScrollPane(c));
public static void main(String[] parameters) {
DrawFrame df = new DrawFrame();
df.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE );
DrawPanel.java
import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
public class DrawPanel extends JPanel {
  JTextArea jTextArea1 = new JTextArea();
  public DrawPanel() {
    this.setSize(this.getMaximumSize());
    this.addMouseListener(new MouseListener() {
      public void mouseClicked(MouseEvent e) {
        drawExample();
      public void mousePressed(MouseEvent e) {
      public void mouseReleased(MouseEvent e) {
      public void mouseEntered(MouseEvent e) {
      public void mouseExited(MouseEvent e) {
  public void paint(Graphics g) {
    // super.paint(g);
    setOpaque(false);
  public Graphics returnGraphics() {
    return this.getGraphics();
  public void drawExample() {
    DrawFrame.ip.sumarea = 0;
    DrawFrame.ip.sumperi = 0;
    DrawFrame.ip.areaT.setText("");
    DrawFrame.ip.periT.setText("");
    Shade.serial = 0;
    for (int i = 0; i < DrawFrame.shades.length; i ++) {
      DrawFrame.shades.number = 0;
this.getGraphics().clearRect(0, 0, this.getSize().width, this.getSize().height);
InfoPanel.info.setText("");
for(int i = 0; i < InfoPanel.shadeindex.size(); i ++) {
try {
Shade oneshade = DrawFrame.shades[Integer.parseInt(InfoPanel.shadeindex.elementAt(i).toString())].returnclass();
oneshade.drawself(this.getGraphics(), this.getVisibleRect().width, this.getVisibleRect().height);
DrawFrame.ip.sumarea += oneshade.returnArea();
DrawFrame.ip.sumperi += oneshade.returnPeri();
DrawFrame.ip.areaT.setText(String.valueOf(DrawFrame.ip.round(DrawFrame.ip.sumarea, 3)));
DrawFrame.ip.periT.setText(String.valueOf(DrawFrame.ip.round(DrawFrame.ip.sumperi, 3)));
} catch (Exception e) {
System.out.println(e.toString());
InfoPanel.java
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
public class InfoPanel extends JPanel {
  static JList shadeList = new JList();
  static JList typeList = new JList();
  static JTextField amountT = new JTextField(10);
  static JButton add = new JButton("add to");
  static JButton remove = new JButton("remove");
  static JButton draw = new JButton("draw");
  static Vector type = new Vector();
  static Vector shadeindex = new Vector(); // ??????????????shades????????
  static JTextField areaT = new JTextField(10);
  static JTextField periT = new JTextField(10);
  static JTextArea info = new JTextArea(10, 10);
  double sumarea;
  double sumperi;
  public InfoPanel() {
    // get information
    JLabel amountL = new JLabel("Enter the amount you want to draw: ");
    JLabel shadeL = new JLabel("The shade you can draw: ");
    shadeList.setVisibleRowCount(5);
    JLabel typeL = new JLabel("The type you want to draw: ");
    typeList.setVisibleRowCount(5);
    // result
    JLabel periL = new JLabel("all perimeters' sum are: ");
    periT.setEditable(false);
    JLabel areaL = new JLabel("all areas' sum are: ");
    areaT.setEditable(false);
    GridBagLayout gbl = new GridBagLayout();
    GridBagConstraints gbc = new GridBagConstraints();
    setLayout(gbl);
    gbc.fill = GridBagConstraints.HORIZONTAL;
    make(amountL, gbl, gbc);
    make(amountT, gbl, gbc);
    gbc.insets = new Insets(10, 0, 0, 0);
    make(shadeL, gbl, gbc);
    gbc.insets = new Insets(0, 0, 0, 0);
    make(new JScrollPane(shadeList), gbl, gbc);
    make(add, gbl, gbc);
    make(typeL, gbl, gbc);
    make(new JScrollPane(typeList), gbl, gbc);
    make(remove, gbl, gbc);
    gbc.insets = new Insets(10, 0, 0, 0);
    make(draw, gbl, gbc);
    gbc.insets = new Insets(0, 0, 0, 0);
    make(areaL, gbl, gbc);
    make(areaT, gbl, gbc);
    make(periL, gbl, gbc);
    make(periT, gbl, gbc);
    make(new JLabel("Each shade's information list here:"), gbl, gbc);
    JScrollPane infojsp = new JScrollPane(info);
    infojsp.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
    infojsp.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
    make(infojsp, gbl, gbc);
    // amountT handle mouse entered event
    amountT.addMouseListener(new MouseListener() {
      public void mouseClicked(MouseEvent e) {
      public void mousePressed(MouseEvent e) {
      public void mouseReleased(MouseEvent e) {
      public void mouseEntered(MouseEvent e) {
        amountT.setText("");
        amountT.requestFocusInWindow(); // ??requestFocus()????????????
      public void mouseExited(MouseEvent e) {
//  add(new JList(new String[]{"1", "2", "3"}));
    this.setSize(this.getPreferredSize());
    add.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        addtoType();
    remove.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        removeType();
    draw.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        draw();
  public void make(Component c, GridBagLayout gbl, GridBagConstraints gbc) {
    gbc.gridx = 0;
    gbl.setConstraints(c, gbc);
    add(c);
  public void addtoType() {
    int[] sindex = shadeList.getSelectedIndices();
    for(int i = 0; i < sindex.length; i ++) {
      if(type.indexOf(DrawFrame.shades[sindex].getName()) == -1) {
type.addElement(DrawFrame.shades[sindex[i]].getName());
shadeindex.addElement(String.valueOf(sindex[i]));
typeList.setListData(type);
typeList.updateUI();
public void removeType() {
int[] tindex = typeList.getSelectedIndices();
String[] temp = new String[tindex.length];
for(int i = 0; i < tindex.length; i ++) {
temp[i] = type.elementAt(tindex[i]).toString();
for(int i = 0; i < tindex.length; i ++) {
type.removeElement(temp[i]);
for(int i = 0; i < temp.length; i ++) {
for(int j = 0; j < DrawFrame.shades.length; j ++) { // ??????????????????????????
if (DrawFrame.shades[j].getName() == temp[i]) {
shadeindex.removeElement(String.valueOf(j));
typeList.setListData(type);
typeList.updateUI();
public void draw() {
long starttime=System.currentTimeMillis(); // ????????????????????
for (int i = 0; i < DrawFrame.shades.length; i ++) {
DrawFrame.shades[i].number = 0;
info.setText("");
int amount;
Shade.serial = 0;
sumarea = 0;
sumperi = 0;
try {
amount = Integer.parseInt(amountT.getText());
} catch (Exception e) {
amount = (int)((Math.random() + 1) * 10); //????????10-20??
amountT.setText("Random produce an int: " + amount);
if (type.size() == 0) { // ????????????????????
for(int i = 0; i < DrawFrame.shades.length; i ++) {
if(type.indexOf(DrawFrame.shades[i].getName()) == -1) {
type.addElement(DrawFrame.shades[i].getName());
shadeindex.addElement(String.valueOf(i));
typeList.setListData(type);
typeList.updateUI();
Graphics g = DrawFrame.dp.getGraphics();
g.clearRect(0, 0, DrawFrame.dp.getSize().width, DrawFrame.dp.getSize().height);
info.append("Each shade Information:\n");
for(int i = 0; i < amount; i ++) {
try {
Shade oneshade = DrawFrame.shades[Integer.parseInt(shadeindex.elementAt((int)(Math.random() * shadeindex.size())).toString())];
oneshade.drawself(g, DrawFrame.dp.getVisibleRect().width, DrawFrame.dp.getVisibleRect().height);
sumarea += oneshade.returnArea();
sumperi += oneshade.returnPeri();
oneshade.areaSum += oneshade.returnArea();
oneshade.periSum += oneshade.returnPeri();
} catch (Exception e) {
System.out.println(e.toString());
info.append("\n");
info.append("Each Type Information:\n");
for(int i = 0; i < shadeindex.size(); i ++) {
Shade eachshade = DrawFrame.shades[Integer.parseInt(shadeindex.elementAt(i).toString())];
String name = eachshade.getName();
int eachsum = eachshade.number;
info.append(eachsum + " " + name + "\n");
info.append(" " + "sum area:" + round(eachshade.areaSum, 3) + "\n");
info.append(" " + "sum peri:" + round(eachshade.periSum, 3) + "\n");
for(int i = 0; i < type.size(); i ++) {
try {
Shade oneshade = DrawFrame.shades[Integer.parseInt(shadeindex.elementAt(i).toString())].returnclass();
oneshade.drawself(g, this.getWidth(), this.getHeight());
sumarea += oneshade.returnArea();
sumperi += oneshade.returnPeri();
} catch (Exception e) {
System.out.println(e.toString());
areaT.setText(String.valueOf(round(sumarea, 3)));
periT.setText(String.valueOf(round(sumperi, 3)));
long endtime=System.currentTimeMillis();
long totaltimetaken=endtime-starttime;//time in milliseconds
info.append("\n");
info.append("Total time used: " + totaltimetaken + " Millis\n");
public double round(double d, int deci) {
double factor = Math.pow(10, deci);
return (Math.round(factor * d))/factor;
Shade.java
import java.awt.*;
public abstract class Shade {
  public double area;
  public double peri;
  static int serial;
  public int number;
  public double areaSum;
  public double periSum;
  abstract public String getName();
  abstract public void drawself(Graphics g, double dpwidth, double dpheight);
  abstract public double returnArea();
  abstract public double returnPeri();
  public Shade returnclass() {
    return this;
}CircleType.java
import java.awt.*;
public class CircleType extends Shade {
  public double r; // ????10??20
  public String getName() {
    return "Circle";
  public void setR() {
    r = (Math.random() + 1) * 10;
  public double returnArea() {
    area = Math.PI * Math.pow(r, 2);
    return area;
  public double returnPeri() {
    peri = 2 * Math.PI * r;
    return peri;
  public void drawself(Graphics g, double dpwidth, double dpheight) {
    setR();
    int x = (int)(dpwidth * Math.random()); // DrawPanel ?????????? ????????????????????
    int y = (int)(dpheight * Math.random());
    if(x < 2 * r) {
      x += 2 * r;
    } else if ( dpwidth - x < 2 * r ) {
      x -= 2 * r;
    if(y < 2 * r) {
      y += 2 * r;
    } else if (- y + 2 * r < dpwidth) {
      y -= 2 * r;
    int width = (int)(2 * r);
    int height = (int)(2 * r);
    g.setColor(Color.blue);
    g.drawOval(x, y, (int)(2 * r), (int)(2 * r));
    g.drawString(String.valueOf(++serial), x + (int)r, y + (int)r);
    InfoPanel.info.append(serial + " is " + "No." + ++ number + " " + getName() + "\n" );
    InfoPanel.info.append("    " + "Area:" + DrawFrame.ip.round(returnArea(), 3) + "\n");
    InfoPanel.info.append("    " + "Peri:" + DrawFrame.ip.round(returnPeri(), 3) + "\n");
    // g.drawString("Area:" + returnArea() + ";" + "Peri:" + returnPeri(), x, y);
}DiamondType.java
import java.awt.*;
public class DiamondType extends Shade {
  public double area;
  public double peri;
  public double w, h; // ??, ??
  public void setWH() {
    w = (Math.random() + 1) * 30;
    h = (Math.random() + 1) * 30;
  public String getName() {
    return "diamond";
  public void drawself(Graphics g, double dpwidth, double dpheight) {
    int x = (int)(dpwidth * Math.random()); // DrawPanel ?????????? ????????????????????
    int y = (int)(dpheight * Math.random());
    setWH();
    if(x < w) {
      x += w;
    } else if ( dpwidth - x < w ) {
      x -= w;
    if(y < h) {
      y += h;
    } else if (- y + h < dpwidth) {
      y -= h;
    g.setColor(Color.darkGray);
    g.drawPolygon(new int[] {x, (int)(x + w/2), (int)(x + w), (int)(x + w/2)}, new int[] {(int)(y + h/2), y, (int)(y + h/2), (int)(y + h)}, 4);
    g.drawString(String.valueOf(++serial), x + (int)(w/2), y + (int)(h/2));
    // g.drawString("iooi's diamond. area:" + returnArea() + ";" + "Peri:" + returnPeri(), x, y);
    InfoPanel.info.append(serial + " is " + "No." + ++ number + " " + getName() + "\n" );
    InfoPanel.info.append("    " + "Area:" + DrawFrame.ip.round(returnArea(), 3) + "\n");
    InfoPanel.info.append("    " + "Peri:" + DrawFrame.ip.round(returnPeri(), 3) + "\n");
  public double returnArea() {
    area = w * h;
    return area/2;
  public double returnPeri() {
    peri = 2 * (w + h);
    return peri * Math.sqrt(2) / 2;
}RectType.java
import java.awt.*;
public class RectType extends Shade {
  public double w, h; // ??, ??
  public String getName() {
    return "Rect";
  public void setWH() {
    w = (Math.random() + 1) * 20;
    h = (Math.random() + 1) * 20;
  public double returnArea() {
    area = w * h;
    return area;
  public double returnPeri() {
    peri = 2 * (w + h);
    return peri;
  public void drawself(Graphics g, double dpwidth, double dpheight) {
    setWH();
    int x = (int)(dpwidth * Math.random()); // DrawPanel ?????????? ????????????????????
    int y = (int)(dpheight * Math.random());
    if(x < w) {
      x += w;
    } else if ( dpwidth - x < w ) {
      x -= w;
    if(y < h) {
      y += h;
    } else if (- y + h < dpwidth) {
      y -= h;
    g.setColor(Color.red);
    g.drawRect(x, y, (int)w, (int)h);
    g.drawString(String.valueOf(++serial), x + (int)(w/2), y + (int)(h/2));
    InfoPanel.info.append(serial + " is " + "No." + ++ number + " " + getName() + "\n" );
    InfoPanel.info.append("    " + "Area:" + DrawFrame.ip.round(returnArea(), 3) + "\n");
    InfoPanel.info.append("    " + "Peri:" + DrawFrame.ip.round(returnPeri(), 3) + "\n");
    // g.drawString("Area:" + returnArea() + ";" + "Peri:" + returnPeri(), x, y);

Answer 1

I really don't want to look through all that code to see how you are doing your painting, I do have some pointers though:
1) Your drawPanel extends JPanel, meaning you should override the paintComponent(Graphics g) and NOT the paint(Graphics g) method. Swing components use paint() to call paintBorder, paintChildren, and paintComponent. If you override the paint then try to use a border or add buttons to the panel then you won't get the correct results. paint() is used for AWT components.
2) To try to answer your question, your paintComponent method should contain ALL YOUR DRAWING. You should not call getGraphics then use that to draw anything on your panel. One thing you can do is create an image the size of the panel, draw on the image wherever you want, then use paintComponent to draw that image.
[You can create an image using component's createImage (width, height) command]
[You would draw on the image buy using the Image getGraphics() method, then drawing on it however you do on any other graphics object]
[You would draw the image to the panel in the paintComponent method using the Graphics g parameter and doing a g.drawImage(...)]