Repaint() doesn't seem to work

Question

I'm just starting to play with 2D graphics, and the repaint method on one of my graphics objects doesn't seem to be working until I resize the outer container.
I have a class called Grid (subclassed from Component) which paints a rectangular grid, and has an inner class called Square (also subclassed from Component). Grid has a 2-D array of Squares. Square has a method setBackColour which changes the background colour and repaints itself. Grid has a method SelectSquare which displays a square a selected by calling setBackColour on the relevant Square.
But when I call SelectSquare nothing happens until I do something which causes the whole of the Grid to be repainted (like resizing it), when the new colour suddenly appears. Why is this?
The code is appended - TestGraphics and GraphPanel were generated by NetBeans so are a bit longer than it need be, and Int2 is just a class with 2 integers for x,y coordinates.
To see what happens, click on any square, and then resize.
Thanks in advance,
Peter
* Grid.java
* Created on 02 August 2006, 15:40
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
package com.ptoye.TestGraphics;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
* @author PToye
public class Grid extends Component {
  private static final int THICK_WIDTH=4;
  private static final int THIN_WIDTH=2;
  private static final int DOTTED_WIDTH=2;
  static  final int SQUARE_SIZE=60;
  private final int START_X=0;
  private final int START_Y=0;
  private static final int SQUARES=3;  //standard sudoku
  private static final int BIGSQUARES=SQUARES*SQUARES;
  private static final int TotalSize=(SQUARES+1)*THICK_WIDTH+SQUARES*(SQUARES-1)*THIN_WIDTH+
      BIGSQUARES*SQUARE_SIZE;
  Square[][] squareArray=new Square[BIGSQUARES][BIGSQUARES] ;
  static Font squareFont=new Font("SansSerif",Font.BOLD,20);
  static final Color NORMAL_BACK_COLOUR=Color.LIGHT_GRAY;
  static final Color SELECTED_BACK_COLOUR=Color.PINK;
   * Creates a new instance of Grid
  public Grid() {
    int currentXCoord=START_X;
    int currentYCoord=START_Y;
    currentXCoord=START_X+THICK_WIDTH;
    int currentXIndex=0;
    for (int BigX = 0; BigX < SQUARES; BigX++) {
      for (int LittleX = 0; LittleX < SQUARES; LittleX++) {
        currentYCoord=START_Y+THICK_WIDTH;
        int currentYIndex=0;
        for (int BigY = 0; BigY < SQUARES; BigY++) {
          for (int LittleY = 0; LittleY < SQUARES; LittleY++) {
            squareArray[currentXIndex][currentYIndex]=
                new Square(currentXCoord,currentYCoord,'4',Color.RED, NORMAL_BACK_COLOUR);
            currentYIndex+=1;
            currentYCoord+=THIN_WIDTH+SQUARE_SIZE;
          currentYCoord+=THICK_WIDTH-THIN_WIDTH;
        currentXIndex+=1;
        currentXCoord+=THIN_WIDTH+SQUARE_SIZE;
      currentXCoord+=THICK_WIDTH-THIN_WIDTH;
  public Dimension getPreferredSize() {
    return new Dimension(TotalSize,TotalSize);
  public void paint(Graphics g) {
    int currentXCoord=START_X;
    int currentYCoord=START_Y;
    int endXCoord=START_X+TotalSize;
    int endYCoord=START_Y+TotalSize;
    Graphics2D g2=(Graphics2D) g;
    g2.setColor(Color.BLACK);
    System.out.println("Painting picture");
    // paint the grid
    for (int BigX = 0; BigX < SQUARES; BigX++) {
      g2.fillRect(currentXCoord,START_Y,THICK_WIDTH,TotalSize);
      g2.fillRect(START_X,currentXCoord,TotalSize,THICK_WIDTH);
      currentXCoord+=THICK_WIDTH+SQUARE_SIZE;
      for (int SmallX = 1; SmallX < SQUARES; SmallX++) {
        g2.fillRect(currentXCoord,START_Y,THIN_WIDTH,TotalSize);
        g2.fillRect(START_X,currentXCoord,TotalSize,THIN_WIDTH);
        currentXCoord+=THIN_WIDTH+SQUARE_SIZE;
    //not forgetting the right & bottom edges
    g2.fillRect(currentXCoord,START_Y,THICK_WIDTH,TotalSize);
    g2.fillRect(START_X,currentXCoord,TotalSize,THICK_WIDTH);
    // paint the squares
    for (int BigX = 0; BigX < BIGSQUARES; BigX++) {
      for (int BigY = 0; BigY < BIGSQUARES; BigY++) {
        squareArray[BigX][BigY].paint(g);
  public Int2 pointToSquare(Point p) {
    double pointX=p.getX();
    double pointY=p.getY();
    int squareX=-1;
    int squareY=-1;
    int currentIndex=0;
    int currentOffset=START_X+THICK_WIDTH;
    searchX:
      for (int i = 0; i < SQUARES; i++) {
        for (int j = 0; j < SQUARES; j++) {
          if (pointX<currentOffset) {
            return null;   // on a black line
          if (pointX<currentOffset+SQUARE_SIZE) {
            squareX=currentIndex;
            break searchX;
          currentOffset+=THIN_WIDTH+SQUARE_SIZE;
          currentIndex++;
        currentOffset+=THICK_WIDTH-THIN_WIDTH;
      if (squareX==-1) {
        return null;
      currentIndex=0;
      currentOffset=START_Y+THICK_WIDTH;
      searchY:
        for (int i = 0; i < SQUARES; i++) {
          for (int j = 0; j < SQUARES; j++) {
            if (pointY<currentOffset) {
              return null;   // on a black line
            if (pointY<currentOffset+SQUARE_SIZE) {
              squareY=currentIndex;
              break searchY;
            currentOffset+=THIN_WIDTH+SQUARE_SIZE;
            currentIndex++;
          currentOffset+=THICK_WIDTH-THIN_WIDTH;
        if (squareY==-1) {
          return null;
        } else {
          return new Int2(squareX,squareY);
  void selectSquare(Int2 squareNos) {
    int x=squareNos.getX();
    int y=squareNos.getY();
    if (x>=0 && x<BIGSQUARES && y>=0 && y<BIGSQUARES) {
      Square s=squareArray[x][y];
      s.setBackColour(SELECTED_BACK_COLOUR);
//      s.repaint();
  void deselectSquare(Int2 squareNos) {
    int x=squareNos.getX();
    int y=squareNos.getY();
    if (x>=0 && x<BIGSQUARES && y>=0 && y<BIGSQUARES) {
      Square s=squareArray[x][y];
      s.setBackColour(NORMAL_BACK_COLOUR);
//      s.repaint();
  class Square extends Component {
    // coordinates of upper left pixel
    private int xCoord;
    private int yCoord;
    private char[] value={' '};
    private Color textColour;
    private Color backColour;
    public Square(int x, int y, char valChar, Color tcol, Color bcol) {
      xCoord=x;
      yCoord=y;
      value[0]=valChar;
      textColour=tcol;
      backColour=bcol;
    public void paint(Graphics g) {
      Graphics2D g2=(Graphics2D) g;
      g2.setFont(squareFont);
      FontMetrics fm=g2.getFontMetrics();
      g2.setColor(backColour);
      g2.fillRect(xCoord,yCoord,Grid.SQUARE_SIZE,Grid.SQUARE_SIZE);
      g2.setColor(textColour);
      int charHeight=fm.getAscent();
      int charWidth=fm.charWidth('0');
      g2.drawString(new String(value),xCoord+Grid.SQUARE_SIZE/2-charWidth/2,
          yCoord+Grid.SQUARE_SIZE/2+charHeight/2);
    public Dimension getPreferredSize() {
      return new Dimension(Grid.SQUARE_SIZE,Grid.SQUARE_SIZE);
    public void setBackColour(Color backColour) {
      this.backColour = backColour;
      repaint();
    public void setTextColour(Color textColour) {
      this.textColour = textColour;
      repaint();
    public void setValue(char value) {
      this.value[0] = value;
      repaint();
* GraphPanel.java
* Created on 02 August 2006, 16:11
package com.ptoye.TestGraphics;
import java.awt.BorderLayout;
import java.awt.Point;
* @author  PToye
public class GraphPanel extends javax.swing.JPanel {
  private Grid p;
  private Int2 selectedSquare;
  /** Creates new form GraphPanel */
  public GraphPanel() {
    initComponents();
    p=new Grid();
    add(p,BorderLayout.CENTER);
    setPreferredSize(p.getPreferredSize());
    selectedSquare=null;
  /** This method is called from within the constructor to
   * initialize the form.
   * WARNING: Do NOT modify this code. The content of this method is
   * always regenerated by the Form Editor.
  private void initComponents() {                         
    FormListener formListener = new FormListener();
    setLayout(new java.awt.BorderLayout());
    setPreferredSize(new java.awt.Dimension(500, 500));
    addMouseListener(formListener);
  // Code for dispatching events from components to event handlers.
  private class FormListener implements java.awt.event.MouseListener {
    public void mouseClicked(java.awt.event.MouseEvent evt) {
      if (evt.getSource() == GraphPanel.this) {
        GraphPanel.this.formMouseClicked(evt);
    public void mouseEntered(java.awt.event.MouseEvent evt) {
    public void mouseExited(java.awt.event.MouseEvent evt) {
    public void mousePressed(java.awt.event.MouseEvent evt) {
    public void mouseReleased(java.awt.event.MouseEvent evt) {
  private void formMouseClicked(java.awt.event.MouseEvent evt) {                                 
    int mouseBtn=evt.getButton();
    Point mousePoint=evt.getPoint();
    if (mouseBtn==evt.BUTTON1) {
      Int2 s=p.pointToSquare(mousePoint);
      if (s!=null) {
        if (selectedSquare!=null) {
          System.out.println("Deselect "+selectedSquare.getX()+selectedSquare.getY());
          p.deselectSquare(selectedSquare);
        selectedSquare=s;
        System.out.println("Select "+selectedSquare.getX()+selectedSquare.getY());
        p.selectSquare(s);
//      p.repaint();
  // Variables declaration - do not modify                    
  // End of variables declaration                  
* Int2.java
* Created on 21 October 2006, 12:01
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
package com.ptoye.TestGraphics;
* @author PToye
public class Int2 {
    private int x;
    private int y;
    Int2(int x, int y ) {
      this.x=x;
      this.y=y;
    public int getX() {
      return x;
    public int getY() {
      return y;
* TestGraphics.java
* Created on 01 August 2006, 22:13
package com.ptoye.TestGraphics;
import java.awt.BorderLayout;
import javax.swing.JPanel;
* @author  PToye
public class TestGraphics extends javax.swing.JFrame {
  private GraphPanel p;
  /** Creates new form TestGraphics */
  public TestGraphics() {
    initComponents();
    p=new GraphPanel();
    setContentPane(p);
    setSize(p.getPreferredSize());
    pack();
  /** This method is called from within the constructor to
   * initialize the form.
   * WARNING: Do NOT modify this code. The content of this method is
   * always regenerated by the Form Editor.
  private void initComponents() {
    jMenuBar1 = new javax.swing.JMenuBar();
    jMenu1 = new javax.swing.JMenu();
    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    setTitle("Testing graphics");
    jMenu1.setText("Menu");
    jMenuBar1.add(jMenu1);
    setJMenuBar(jMenuBar1);
    pack();
   * @param args the command line arguments
  public static void main(String args[]) {
    java.awt.EventQueue.invokeLater(new Runnable() {
      public void run() {
        new TestGraphics().setVisible(true);
  // Variables declaration - do not modify
  private javax.swing.JMenu jMenu1;
  private javax.swing.JMenuBar jMenuBar1;
  // End of variables declaration
}

Answer 1

Here's a way to implement your gui in the two ways mentioned above:
GridG � graphics approach with limited redrawing for de/selections
GridC � component approach where the AWT does a lot of the work.
This second approach resizes okay.
Everything has been changed to Swing � lightweight components. One difficulty with
mixing lightweight and heavyweight components is that the heavyweight components are
rendered above/over/on top of the lightweight components. So, for example, the Grid class
extending Component is a heavyweight component and will be rendered over any JMenus and
JMenuItems that extend below the JMenuBar in the JMenu popupMenu during menu selections,
when you add them, of course. The Grid component will hide/obscure the JMenu lightweight
components.
The Int2 class remains unchanged. I did not use the GraphPanel class.
import java.awt.*;
import javax.swing.*;
public class TG extends JFrame {
    private GridG gridG;
    private GridC gridC;
    public TG() {
        setTitle("Testing graphics");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setJMenuBar(getMenus());
        gridG = new GridG();
        gridC = new GridC();
        JTabbedPane tabbedPane = new JTabbedPane();
        tabbedPane.addTab("graphics", gridG);
        tabbedPane.addTab("component", gridC);
        setContentPane(tabbedPane);
        pack();
        setLocation(200,50);
    private JMenuBar getMenus() {
        JMenu jMenu1 = new JMenu("Menu");
        JMenuBar menuBar = new JMenuBar();
        menuBar.add(jMenu1);
        return menuBar;
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                new TG().setVisible(true);
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class GridG extends JPanel {
    private static final int THICK_WIDTH  =  4;
    private static final int THIN_WIDTH   =  2;
    private static final int DOTTED_WIDTH =  2;
    static         final int SQUARE_SIZE  = 60;
    private        final int START_X      =  0;
    private        final int START_Y      =  0;
    private static final int SQUARES      =  3;  //standard sudoku
    private static final int BIGSQUARES = SQUARES*SQUARES;
    private static final int TotalSize=
                 (SQUARES+1)*THICK_WIDTH+SQUARES*(SQUARES-1)*THIN_WIDTH+
                                    BIGSQUARES*SQUARE_SIZE;
    Square[][] squareArray = new Square[BIGSQUARES][BIGSQUARES];
    static Font squareFont = new Font("SansSerif",Font.BOLD,20);
    static final Color NORMAL_BACK_COLOUR   = Color.LIGHT_GRAY;
    static final Color SELECTED_BACK_COLOUR = Color.PINK;
    public GridG() {
        int currentXCoord=START_X;
        int currentYCoord=START_Y;
        currentXCoord=START_X+THICK_WIDTH;
        int currentXIndex=0;
        for (int BigX = 0; BigX < SQUARES; BigX++) {
            for (int LittleX = 0; LittleX < SQUARES; LittleX++) {
                currentYCoord=START_Y+THICK_WIDTH;
                int currentYIndex=0;
                for (int BigY = 0; BigY < SQUARES; BigY++) {
                    for (int LittleY = 0; LittleY < SQUARES; LittleY++) {
                        squareArray[currentXIndex][currentYIndex]=
                            new Square(currentXCoord,currentYCoord,'4',
                                       Color.RED, NORMAL_BACK_COLOUR);
                        currentYIndex+=1;
                        currentYCoord+=THIN_WIDTH+SQUARE_SIZE;
                    currentYCoord+=THICK_WIDTH-THIN_WIDTH;
                currentXIndex+=1;
                currentXCoord+=THIN_WIDTH+SQUARE_SIZE;
            currentXCoord+=THICK_WIDTH-THIN_WIDTH;
        addMouseListener(ml);
        setBackground(Color.BLACK);
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2=(Graphics2D) g;
        // paint the squares
        for (int BigX = 0; BigX < BIGSQUARES; BigX++) {
            for (int BigY = 0; BigY < BIGSQUARES; BigY++) {
                squareArray[BigX][BigY].draw(g);
    public Dimension getPreferredSize() {
        return new Dimension(TotalSize,TotalSize);
    /** This could easily become an outer class. */
    private class Square {
        // coordinates of upper left pixel
        private int xCoord;
        private int yCoord;
        private char[] value={' '};
        private Color textColour;
        private Color backColour;
        public Square(int x, int y, char valChar, Color tcol, Color bcol) {
            xCoord=x;
            yCoord=y;
            value[0]=valChar;
            textColour=tcol;
            backColour=bcol;
        public void draw(Graphics g) {
            Graphics2D g2=(Graphics2D) g;
            g2.setFont(squareFont);
            FontMetrics fm=g2.getFontMetrics();
            g2.setColor(backColour);
            g2.fillRect(xCoord,yCoord,Grid.SQUARE_SIZE,Grid.SQUARE_SIZE);
            g2.setColor(textColour);
            int charHeight=fm.getAscent();
            int charWidth=fm.charWidth('0');
            g2.drawString(new String(value),xCoord+Grid.SQUARE_SIZE/2-charWidth/2,
                                            yCoord+Grid.SQUARE_SIZE/2+charHeight/2);
        public void setBackColour(Color backColour) {
            this.backColour = backColour;
        public void setTextColour(Color textColour) {
            this.textColour = textColour;
        public void setValue(char value) {
            this.value[0] = value;
    /** Ths could become an outer class */
    private MouseListener ml = new MouseAdapter() {
        private Int2 selectedSquare;
        public void mousePressed(MouseEvent e) {
            Point mousePoint = e.getPoint();
            Int2 s = pointToSquare(mousePoint);
            if (s != null) {
                if (selectedSquare != null) {
                    System.out.println("Deselect " + selectedSquare.getX()
                                                   + selectedSquare.getY());
                    int x = selectedSquare.getX();
                    int y = selectedSquare.getY();
                    squareArray[x][y].setBackColour(NORMAL_BACK_COLOUR);
                    squareArray[x][y].draw(getGraphics());
                selectedSquare = s;
                System.out.println("Select " + selectedSquare.getX()
                                             + selectedSquare.getY());
                int x = s.getX();
                int y = s.getY();
                squareArray[x][y].setBackColour(SELECTED_BACK_COLOUR);
                squareArray[x][y].draw(getGraphics());
        private Int2 pointToSquare(Point p) {
            double pointX=p.getX();
            double pointY=p.getY();
            int squareX=-1;
            int squareY=-1;
            int currentIndex=0;
            int currentOffset=START_X+THICK_WIDTH;
            searchX:
                for (int i = 0; i < SQUARES; i++) {
                    for (int j = 0; j < SQUARES; j++) {
                        if (pointX<currentOffset) {
                            return null;   // on a black line
                        if (pointX < currentOffset+SQUARE_SIZE) {
                            squareX=currentIndex;
                            break searchX;
                        currentOffset+=THIN_WIDTH+SQUARE_SIZE;
                        currentIndex++;
                    currentOffset+=THICK_WIDTH-THIN_WIDTH;
            if (squareX==-1) {
                return null;
            currentIndex=0;
            currentOffset=START_Y+THICK_WIDTH;
            searchY:
                for (int i = 0; i < SQUARES; i++) {
                    for (int j = 0; j < SQUARES; j++) {
                        if (pointY<currentOffset) {
                            return null;   // on a black line
                        if (pointY < currentOffset+SQUARE_SIZE) {
                            squareY=currentIndex;
                            break searchY;
                        currentOffset += THIN_WIDTH+SQUARE_SIZE;
                        currentIndex++;
                    currentOffset += THICK_WIDTH-THIN_WIDTH;
            if (squareY==-1) {
                return null;
            } else {
                return new Int2(squareX,squareY);
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class GridC extends JPanel {
    private static final int THICK_WIDTH  =  4;
    private static final int THIN_WIDTH   =  2;
    static         final int SQUARE_SIZE  = 60;
    private static final int SQUARES      =  3;  //standard sudoku
    private static final int BIGSQUARES = SQUARES*SQUARES;
    private static final int TotalSize  =
                 (SQUARES+1)*THICK_WIDTH+SQUARES*(SQUARES-1)*THIN_WIDTH+
                         BIGSQUARES*SQUARE_SIZE;
    Square[][] squareArray = new Square[BIGSQUARES][BIGSQUARES] ;
    static Font squareFont = new Font("SansSerif",Font.BOLD,20);
    static final Color NORMAL_BACK_COLOUR   = Color.LIGHT_GRAY;
    static final Color SELECTED_BACK_COLOUR = Color.PINK;
    public GridC() {
        setBackground(Color.black);
        GridBagLayout gridbag = new GridBagLayout();
        GridBagConstraints gbc = new GridBagConstraints();
        int[] gws = { 1, GridBagConstraints.RELATIVE, GridBagConstraints.REMAINDER };
        setLayout(gridbag);
        for (int j = 0; j < BIGSQUARES; j++) {
            JPanel cell = new JPanel(gridbag);
            cell.setBackground(Color.black);
            gbc.insets = new Insets(1,1,1,1);
            for (int k = 0; k < BIGSQUARES; k++) {
                int val = j*BIGSQUARES + k + 1;
                squareArray[j][k]= new Square(val, Color.RED, NORMAL_BACK_COLOUR);
                squareArray[j][k].addMouseListener(ml);
                gbc.gridwidth = gws[k % gws.length];
                cell.add(squareArray[j][k], gbc);
            gbc.insets = new Insets(0,0,0,0);
            if(j/3 < 2)       gbc.insets.bottom = 2;
            if((j+1) % 3 > 0) gbc.insets.right = 2;
            gbc.gridwidth = gws[j % gws.length];
            add(cell, gbc);
    public Dimension getPreferredSize() {
        return new Dimension(TotalSize, TotalSize);
    private class Square extends JPanel {
        String value;
        private Color textColour;
        private Color backColour;
        public Square(int val, Color tcol, Color bcol) {
            value = String.valueOf(val);
            textColour=tcol;
            backColour=bcol;
        protected void paintComponent(Graphics g) {
            Graphics2D g2=(Graphics2D) g;
            g2.setFont(squareFont);
            FontMetrics fm=g2.getFontMetrics();
            g2.setColor(backColour);
            g2.fillRect(0,0,Grid.SQUARE_SIZE,Grid.SQUARE_SIZE);
            g2.setColor(textColour);
            int charHeight=fm.getAscent();
            int charWidth=fm.stringWidth(value);
            g2.drawString(value, Grid.SQUARE_SIZE/2-charWidth/2,
                                 Grid.SQUARE_SIZE/2+charHeight/2);
        public Dimension getPreferredSize() {
            return new Dimension(Grid.SQUARE_SIZE,Grid.SQUARE_SIZE);
        public void setBackColour(Color backColour) {
            this.backColour = backColour;
            repaint();
        public void setTextColour(Color textColour) {
            this.textColour = textColour;
            repaint();
        public void setValue(int value) {
            this.value = String.valueOf(value);
            repaint();
    private MouseListener ml = new MouseAdapter() {
        private Square selectedSquare;
        public void mousePressed(MouseEvent e) {
            Square square = (Square)e.getSource();
            if (selectedSquare != null)
                selectedSquare.setBackColour(NORMAL_BACK_COLOUR);
            square.setBackColour(SELECTED_BACK_COLOUR);
            selectedSquare = square;
}