Resize the panel without revalidation

Question

I have aJPanel in which I draw lines to create an illusion of pencil. This panel is in aScrollPane.

When I resize the panel one call to revalidate() method is automatically placed and all my drawn lines in this panel are gone. Is there any way to keep my drawn line in the panel with the new size ?

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.AdjustmentEvent;
import java.awt.event.AdjustmentListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
/**
 *
 * @author Sanjeev
 */
public class WorkArea extends JFrame implements ActionListener, MouseListener, MouseMotionListener 
{
 private final int  PEN_OP         = 1;
 private final int  ERASER_OP      = 2;
 private final int  SCROLL_OP      = 3;
 private int mousex                = 0;
 private int mousey                = 0;
 private int prevx                 = 0;
 private int prevy                 = 0;
 private boolean initialPen        = true;
 private boolean initialEraser     = true;
 private int  eraserLength         = 5;
 private int    opStatus           = PEN_OP;
 private Color  mainColor          = new Color(0,0,0);
 private int drawPanelHeight       =1000;

    public WorkArea()
    {
        initComponents();
        setLocationRelativeTo(null);
        pencilButton.addActionListener(this);
        eraserButton.addActionListener(this);
        drawPanel.addMouseMotionListener(this);
        drawPanel.addMouseListener(this);
        drawPanel.add(new TestPane());
        this.addMouseListener(this);
        this.addMouseMotionListener(this);
    }

    private void initComponents() {

        headerPanel = new javax.swing.JPanel();
        backButton = new javax.swing.JLabel();
        headerImage = new javax.swing.JLabel();
        controlPanel = new javax.swing.JPanel();
        scrollButton = new javax.swing.JButton();
        pencilButton = new javax.swing.JButton();
        eraserButton = new javax.swing.JButton();
        drawingPanel = new javax.swing.JPanel();
        drawingScrollPane = new javax.swing.JScrollPane();
        drawPanel = new javax.swing.JPanel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("v0.1");
        setBackground(new java.awt.Color(237, 254, 255));
        setBounds(new java.awt.Rectangle(0, 0, 513, 693));
        setResizable(false);

        headerPanel.setBackground(new java.awt.Color(237, 254, 255));
        headerPanel.setPreferredSize(new java.awt.Dimension(513, 25));
        headerPanel.setLayout(null);

        backButton.setBackground(new java.awt.Color(237, 254, 255));
        backButton.setFont(new java.awt.Font("Tahoma", 0, 10)); // NOI18N
        backButton.setForeground(new java.awt.Color(255, 255, 255));
        backButton.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/back-arrow.png"))); // NOI18N
        backButton.setText("Back");
        backButton.setHorizontalTextPosition(javax.swing.SwingConstants.CENTER);
        backButton.setPreferredSize(new java.awt.Dimension(40, 20));
        headerPanel.add(backButton);
        backButton.setBounds(0, 3, 40, 20);

        headerImage.setBackground(new java.awt.Color(237, 254, 255));
        headerImage.setFont(new java.awt.Font("Tahoma", 1, 14)); // NOI18N
        headerImage.setForeground(new java.awt.Color(255, 255, 255));
        headerImage.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/topbar_ipad_wide.png"))); // NOI18N
        headerImage.setText("Work Area");
        headerImage.setHorizontalTextPosition(javax.swing.SwingConstants.CENTER);
        headerImage.setPreferredSize(new java.awt.Dimension(513, 25));
        headerPanel.add(headerImage);
        headerImage.setBounds(0, 0, 513, 25);

        controlPanel.setBackground(new java.awt.Color(237, 254, 255));
        controlPanel.setPreferredSize(new java.awt.Dimension(90, 670));
        controlPanel.setLayout(null);

        scrollButton.setBackground(new java.awt.Color(237, 254, 255));
        scrollButton.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/up_down_ipad.png"))); // NOI18N
        scrollButton.setPreferredSize(new java.awt.Dimension(60, 60));
        scrollButton.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                scrollButtonMouseClicked(evt);
            }
        });
        controlPanel.add(scrollButton);
        scrollButton.setBounds(20, 570, 60, 60);

        pencilButton.setBackground(new java.awt.Color(237, 254, 255));
        pencilButton.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/pencil_ipad.png"))); // NOI18N
        pencilButton.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                pencilButtonMouseClicked(evt);
            }
        });
        controlPanel.add(pencilButton);
        pencilButton.setBounds(20, 450, 60, 60);

        eraserButton.setBackground(new java.awt.Color(237, 254, 255));
        eraserButton.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/eraser_ipad.png"))); // NOI18N
        eraserButton.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                eraserButtonMouseClicked(evt);
            }
        });
        controlPanel.add(eraserButton);
        eraserButton.setBounds(20, 510, 60, 60);

        drawingPanel.setBackground(new java.awt.Color(237, 254, 255));
        drawingPanel.setPreferredSize(new java.awt.Dimension(420, 670));
        drawingPanel.setLayout(null);

        drawingScrollPane.setBorder(null);
        drawingScrollPane.setPreferredSize(new java.awt.Dimension(423, 1000));

        drawPanel.setBackground(new java.awt.Color(237, 254, 255));
        drawPanel.setPreferredSize(new java.awt.Dimension(400, 1000));
        drawPanel.setLayout(null);
        drawingScrollPane.setViewportView(drawPanel);

        drawingPanel.add(drawingScrollPane);
        drawingScrollPane.setBounds(0, 0, 424, 670);

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 513, Short.MAX_VALUE)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(headerPanel, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.PREFERRED_SIZE, 513, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(layout.createSequentialGroup()
                    .addComponent(controlPanel, javax.swing.GroupLayout.PREFERRED_SIZE, 90, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addGap(0, 423, Short.MAX_VALUE)))
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                    .addGap(0, 93, Short.MAX_VALUE)
                    .addComponent(drawingPanel, javax.swing.GroupLayout.PREFERRED_SIZE, 420, javax.swing.GroupLayout.PREFERRED_SIZE)))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 693, Short.MAX_VALUE)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(layout.createSequentialGroup()
                    .addComponent(headerPanel, javax.swing.GroupLayout.PREFERRED_SIZE, 25, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addGap(0, 668, Short.MAX_VALUE)))
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                    .addGap(0, 23, Short.MAX_VALUE)
                    .addComponent(controlPanel, javax.swing.GroupLayout.PREFERRED_SIZE, 670, javax.swing.GroupLayout.PREFERRED_SIZE)))
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                    .addGap(0, 23, Short.MAX_VALUE)
                    .addComponent(drawingPanel, javax.swing.GroupLayout.PREFERRED_SIZE, 670, javax.swing.GroupLayout.PREFERRED_SIZE)))
        );

        pack();
    }                      

    @Override
    public void actionPerformed(ActionEvent e) 
    {
       if (e.getActionCommand() == "Pen")
       opStatus = PEN_OP;

       if (e.getActionCommand() == "Eraser")
       opStatus = ERASER_OP;

       if(e.getActionCommand() == "Scroll")
       opStatus = SCROLL_OP;
    }

    private void pencilButtonMouseClickedTest(java.awt.event.MouseEvent evt) 
    {                                         
        opStatus = PEN_OP;
        Graphics g  = drawPanel.getGraphics();

      if (initialPen)
      {  
       setGraphicalDefaults(evt);
       initialPen = false;
       g.drawLine(prevx,prevy,mousex,mousey);
      }
      if (mouseHasMoved(evt))
      {  
       mousex = evt.getX();
       mousey = evt.getY();
       g.drawLine(prevx,prevy,mousex,mousey);
       prevx = mousex;
       prevy = mousey;
      }
    } 

    private void eraserButtonMouseClickedTest(java.awt.event.MouseEvent evt)
    {
       opStatus = ERASER_OP;
       Graphics g  = drawPanel.getGraphics();

      if (initialEraser)
      {  
       setGraphicalDefaults(evt);
       initialEraser = false;
       mousex = evt.getX();
       mousey = evt.getY();
       System.out.println("Initial Eraser ::::::::x's value is : "+prevx+" , "+mousey+" and y's value is : "+mousex+" , "+mousey);
       g.setColor(new java.awt.Color(237,254,255));
       g.fillRect(mousex-eraserLength, mousey-eraserLength,eraserLength*2,eraserLength*2);
       //g.setColor(Color.black); //Eraser Border
       g.drawRect(mousex-eraserLength,mousey-eraserLength,eraserLength*2,eraserLength*2);
       prevx = mousex;
       prevy = mousey;
      }

      if (mouseHasMoved(evt))
      {
       System.out.println("Eraser ::::::::x's value is : "+prevx+" , "+mousey+" and y's value is : "+mousex+" , "+mousey);
       g.setColor(new java.awt.Color(237,254,255));
       g.drawRect(prevx-eraserLength, prevy-eraserLength,eraserLength*2,eraserLength*2);

       mousex  = evt.getX();
       mousey  = evt.getY();

       /* Draw eraser block to panel */
       g.setColor(new java.awt.Color(237,254,255));
       g.fillRect(mousex-eraserLength, mousey-eraserLength,eraserLength*2,eraserLength*2);
       g.setColor(Color.black);//Eraser Border
       g.drawRect(mousex-eraserLength,mousey-eraserLength,eraserLength*2,eraserLength*2);
       prevx = mousex;
       prevy = mousey;
      }
    }


    private void scrollButtonMouseClicked(java.awt.event.MouseEvent evt) {                                          
      opStatus = SCROLL_OP;
      drawingScrollPane.getVerticalScrollBar().addAdjustmentListener(new AdjustmentListener() {

      @Override
      public void adjustmentValueChanged(AdjustmentEvent e) 
      {
        int extent,curValue;
        extent = drawingScrollPane.getVerticalScrollBar().getModel().getExtent();
        curValue = drawingScrollPane.getVerticalScrollBar().getValue()+extent;
        if(curValue==drawPanel.getHeight())
        {
        System.out.println("value of scroll equals to Max value....");
        drawPanel.setPreferredSize(new Dimension(423,drawPanelHeight*4));       
        }
        System.out.println("Value: " + curValue + " Max: " + drawingScrollPane.getVerticalScrollBar().getMaximum());
      }
      });
    }                                         

    private void eraserButtonMouseClicked(java.awt.event.MouseEvent evt) {                                          
       eraserButtonMouseClickedTest(evt);
       updateMouseCoordinates(evt);
    }                                         

    private void pencilButtonMouseClicked(java.awt.event.MouseEvent evt) {                                          
       opStatus = PEN_OP;

    }                                         




  public boolean mouseHasMoved(MouseEvent e)
   {
    return (mousex != e.getX() || mousey != e.getY());
   }

 public void setGraphicalDefaults(MouseEvent e)
 {
    mousex   = e.getX();
    mousey   = e.getY();
    prevx    = e.getX();
    prevy    = e.getY();
 }

 @Override
    public void mouseDragged(MouseEvent e)
    {
        updateMouseCoordinates(e);

       switch (opStatus)
       {
          case PEN_OP   : pencilButtonMouseClickedTest(e);
                          break;
          case ERASER_OP: eraserButtonMouseClicked(e);
                          break;
          case SCROLL_OP: scrollButtonMouseClicked(e);
                          break;
       }
    }

    public void mouseReleased(MouseEvent e)
    {  
        updateMouseCoordinates(e);

       switch (opStatus)
       {
          case PEN_OP    : releasedPen();
                           break;
          case ERASER_OP : releasedEraser();
                           break;
       }
    }

   public void mouseEntered(MouseEvent e)
   {
    updateMouseCoordinates(e);
   }

   public void releasedPen()
   {
    initialPen = true;
   }

    public void releasedEraser()
    {
    initialEraser = true;
    Graphics g  = drawPanel.getGraphics();
    g.setColor(mainColor.white);
    g.drawRect(mousex-eraserLength,mousey-eraserLength,eraserLength*2,eraserLength*2);
    }

    public void updateMouseCoordinates(MouseEvent e)
    {
    String xCoor ="";
    String yCoor ="";

    if (e.getX() < 0) xCoor = "0";
    else
    {
       xCoor = String.valueOf(e.getX());
    }

    if (e.getY() < 0) xCoor = "0";
    else
    {
       yCoor = String.valueOf(e.getY());
    }
   }

    public static void main(String args[]) {
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(WorkArea.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(WorkArea.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(WorkArea.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(WorkArea.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }

        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new WorkArea().setVisible(true);
            }
        });
    }                   
    private javax.swing.JLabel backButton;
    private javax.swing.JPanel controlPanel;
    private javax.swing.JPanel drawPanel;
    private javax.swing.JPanel drawingPanel;
    private javax.swing.JScrollPane drawingScrollPane;
    private javax.swing.JButton eraserButton;
    private javax.swing.JLabel headerImage;
    private javax.swing.JPanel headerPanel;
    private javax.swing.JButton pencilButton;
    private javax.swing.JButton scrollButton;             

    @Override
    public void mouseClicked(MouseEvent e) {

    }

     @Override
    public void mouseExited(MouseEvent e) {
        updateMouseCoordinates(e);
    }

     @Override
    public void mouseMoved(MouseEvent e) {
        updateMouseCoordinates(e);
    }

    @Override
    public void mousePressed(MouseEvent e) {
        updateMouseCoordinates(e);
    }
}

Which part of **Do not use component.getGraphics** is so hard to understand? — kleopatra, Sep 03 '13 at 10:03
@kleopatra From component.getGraphics you'll not able to persist the drawing on the panel when some property like size changes !! For that you need to use paintComponent method. But this technique has its own limitations too !! — Neo, Sep 03 '13 at 10:10
@kleopatra I think instead of pressing the +ve button you have pressed-ve button ! — Neo, Sep 03 '13 at 10:16

score 4 · Answer 1 · edited May 23 '17 at 11:53

I assume you are drawing to the JPanel by using getGraphics() and rendering your out put to it.

You have now seen why you shouldn't do this. When the component is repainted, anything previously painted to is wiped cleaned and you are expected to repaint the contents.

Start by overriding paintComponent and updating all the lines within this method (don't forget to call super.paintComponent

See Performing Custom Painting and Painting in AWT and Swing for more details

For example..

Updated with example

This is a modified version of the answer to MouseEvent is not registering a release when I release the mouse button which includes a scroll pane...

enter image description here

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.UIManager;

public class MouseDraggedTest {

    public static void main(String[] args) {
        new MouseDraggedTest();
    }

    public MouseDraggedTest() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new JScrollPane(new TestPane()));
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private Map<Point, List<Point>> mapPoints;
        private Point currentPoint;

        public TestPane() {
            mapPoints = new HashMap<>(25);
            MouseAdapter mouseListener = new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent e) {
                    currentPoint = e.getPoint();
                    mapPoints.put(currentPoint, new ArrayList<Point>(25));
                }

                @Override
                public void mouseReleased(MouseEvent e) {
                    List<Point> points = mapPoints.get(currentPoint);
                    if (points.isEmpty()) {
                        mapPoints.remove(currentPoint);
                    }
                    currentPoint = null;
                }

                @Override
                public void mouseDragged(MouseEvent me) {
                    List<Point> points = mapPoints.get(currentPoint);
                    points.add(me.getPoint());
                    repaint();
                }
            };
            addMouseListener(mouseListener);
            addMouseMotionListener(mouseListener);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 800);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);

            for (Point startPoint : mapPoints.keySet()) {
                List<Point> points = mapPoints.get(startPoint);
                for (Point p : points) {
                    if (startPoint != null) {
                        g.drawLine(startPoint.x, startPoint.y, p.x, p.y);
                    }
                    startPoint = p;
                }
            }
        }
    }
}

Updated with a BufferedImage example

Because you need to supply more operations than just drawing, you may find it easier to use BufferedImage as your primary drawing surface and render this to your DrawingPanel

enter image description here

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Point;
import java.awt.Shape;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;
import java.awt.image.BufferedImage;
import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JToggleButton;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class MyPicture {

    public static void main(String[] args) {
        new MyPicture();
    }

    public MyPicture() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public enum DrawOperation {

        Draw,
        Erase

    }

    public class TestPane extends JPanel {

        private DrawOperation op;

        private JToggleButton pencil;
        private JToggleButton eraser;

        private DrawPane drawPane;

        public TestPane() {
            setLayout(new BorderLayout());

            drawPane = new DrawPane();

            MouseAdapter adapter = new MouseAdapter() {

                private Point startPoint;

                @Override
                public void mouseEntered(MouseEvent e) {
                    drawPane.updateDrawCursor(e.getPoint(), op);
                }

                @Override
                public void mouseExited(MouseEvent e) {
                    drawPane.removeDrawCursor();
                }

                @Override
                public void mousePressed(MouseEvent e) {
                    startPoint = e.getPoint();
                }

                @Override
                public void mouseReleased(MouseEvent e) {
                    startPoint = null;
                }

                @Override
                public void mouseDragged(MouseEvent e) {
                    drawPane.applyOperation(startPoint, e.getPoint(), op);
                    drawPane.updateDrawCursor(e.getPoint(), op);
                    startPoint = e.getPoint();
                }

                @Override
                public void mouseMoved(MouseEvent e) {
                    drawPane.updateDrawCursor(e.getPoint(), op);
                }

            };

            drawPane.addMouseListener(adapter);
            drawPane.addMouseMotionListener(adapter);

            JPanel operations = new JPanel(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridwidth = GridBagConstraints.REMAINDER;

            pencil = new JToggleButton("Draw");
            eraser = new JToggleButton("Erase");

            ButtonGroup bgOps = new ButtonGroup();
            bgOps.add(pencil);
            bgOps.add(eraser);

            operations.add(pencil, gbc);
            operations.add(eraser, gbc);

            pencil.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    op = DrawOperation.Draw;
                }
            });

            eraser.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    op = DrawOperation.Erase;
                }
            });

            add(operations, BorderLayout.WEST);
            add(new JScrollPane(drawPane));
        }

    }

    public class DrawPane extends JPanel {

        private BufferedImage image;
        private Shape drawCursor;
        private Point cursorPoint;

        private int eraseSize = 20;

        public DrawPane() {
            image = new BufferedImage(400, 400, BufferedImage.TYPE_INT_RGB);
            Graphics2D g2d = image.createGraphics();
            g2d.setBackground(Color.WHITE);
            g2d.fillRect(0, 0, 400, 400);
            g2d.dispose();
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            if (image != null) {
                g2d.drawImage(image, 0, 0, this);
            }
            if (drawCursor != null && cursorPoint != null) {
                int x = (cursorPoint.x - (drawCursor.getBounds().width) / 2);
                int y = (cursorPoint.y - (drawCursor.getBounds().height) / 2);
                g2d.translate(x, y);
                g2d.draw(drawCursor);
                g2d.translate(-x, -y);
            }
            g2d.dispose();
        }

        public void updateDrawCursor(Point point, DrawOperation op) {
            cursorPoint = point;
            if (op != null) {
                switch (op) {
                    case Draw:
                        drawCursor = new Ellipse2D.Float(0, 0, 4, 4);
                        break;
                    case Erase:
                        drawCursor = new Ellipse2D.Float(0, 0, eraseSize, eraseSize);
                        break;
                }
            } else {
                drawCursor = null;
            }
            repaint();
        }

        protected void removeDrawCursor() {
            drawCursor = null;
            repaint();
        }

        protected void applyOperation(Point fromPoint, Point toPoint, DrawOperation op) {
            if (image != null) {

                if (op != null) {
                    Graphics2D g2d = image.createGraphics();
                    switch (op) {
                        case Draw:
                            g2d.setColor(Color.BLACK);
                            g2d.draw(new Line2D.Float(fromPoint, toPoint));
                            break;
                        case Erase:
                            g2d.setColor(Color.WHITE);
                            g2d.setStroke(new BasicStroke(eraseSize));
                            g2d.draw(new Line2D.Float(fromPoint, toPoint));
                            break;
                    }
                    g2d.dispose();
                }

            }
            repaint();
        }
    }
}

Sir can we add this code in already created JPanel like drawPanel ? Because I'm facing problem in paintComponent() method when I write drawPanel.paintComponent(g); It says that paintComponent(Graphics) has protected access in JComponent. — Neo, Aug 30 '13 at 11:35
You should never call paintComponent yourself. It will be called by the RepaintManager automatically. Have you read through the supplied links? — MadProgrammer, Aug 30 '13 at 11:42
Now I'm reading those links. Before that I was just try to implement it as soon as possible. — Neo, Aug 30 '13 at 12:19
But when I call it from my panel by myPanel.add(new TestPane()); then the background color is still not what I have set on this JPanel. Wny ? — Neo, Sep 02 '13 at 11:43
I've also given you links to two runnable examples. Until you provide me with an example of what and how you are painting, it's pointless for me to spend the time putting another example together to just have you tell me it's not what you want. Show me how you are working and provide me with some details about what it is you are trying to achieve and then we can work together to find a solution — MadProgrammer, Sep 02 '13 at 21:37
Now I have provided the screen shot of what I intended to do. When I scroll down and then scroll up again all my drawing which are invisible when I scroll down are gone but I want to persist that drawing on my panel. Please help me to solve this problem. — Neo, Sep 03 '13 at 06:15
The screen shot is nice, but unless you can provide with the `paint` routines or a runnable example, I can't see how I can help you... — MadProgrammer, Sep 03 '13 at 06:17
Thank you very much...but the limitation with this code is that we cannot define the size of scroll bar and we can't change the background color of this scroll bar. — Neo, Sep 03 '13 at 06:36
It's my project's requirement. Now I have provided my code. I was trying to implement how you have implemented in your example. But it's working in this scenario ! — Neo, Sep 03 '13 at 06:40
You are using Nimbus look and feel, I'm using the system look and feel, how does this change how painting is done in Swing? — MadProgrammer, Sep 03 '13 at 06:40
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/36702/discussion-between-neo-and-madprogrammer) — Neo, Sep 03 '13 at 06:44
But sir in this example to see the scroll bar we have to manually decrease the size of frame. It's not appearing automatically when the program ran ! — Neo, Sep 03 '13 at 10:20
Don't use pack, use set size. Use the Scrollable interface the define the preferred scrollable size, which should be smaller the preferred size of the component — MadProgrammer, Sep 03 '13 at 19:55

Resize the panel without revalidation

1 Answers1

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