1

Im working on a paint application written in java and running into a few (more) problems. I have a gui and a working program(kinda), my only problem is that the lines and graphics that the user draws are not saved(disappear after next one is drawn).

From a past question i learned that i will need to use a BufferedImage to store the drawings then paint that inside my paint class.

My questions are, Can anyone provide a basic explanation/example of how to use a bufferedimage to store and paint the drawing and if i need to, how will i pass the color and thickness of the drawn line into a stored array.

thats my whole class.

package javapaint;

import java.awt.*;
import javax.swing.*;

public class JavaPaintUI extends javax.swing.JFrame {

/** Creates new form JavaPaintUI */
public JavaPaintUI() {
    initComponents();
}

// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    buttonGroup1 = new javax.swing.ButtonGroup();
    buttonGroup2 = new javax.swing.ButtonGroup();
    jPanel4 = new javax.swing.JPanel();
    jRadioButton9 = new javax.swing.JRadioButton();
    jRadioButton10 = new javax.swing.JRadioButton();
    jSlider2 = new javax.swing.JSlider();
    jLabel1 = new javax.swing.JLabel();
    jPanel2 = new Panel2();
    jPanel3 = new javax.swing.JPanel();
    jRadioButton3 = new javax.swing.JRadioButton();
    jRadioButton4 = new javax.swing.JRadioButton();
    jRadioButton5 = new javax.swing.JRadioButton();
    jRadioButton6 = new javax.swing.JRadioButton();
    jRadioButton7 = new javax.swing.JRadioButton();
    jRadioButton8 = new javax.swing.JRadioButton();
    jButton1 = new javax.swing.JButton();
    jButton2 = new javax.swing.JButton();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    setTitle("JavaPaint ~ Nick R");

    jPanel4.setBorder(javax.swing.BorderFactory.createTitledBorder("Tool"));

    buttonGroup1.add(jRadioButton9);
    jRadioButton9.setText("Pen");
    jRadioButton9.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jRadioButton9ActionPerformed(evt);
        }
    });

    buttonGroup1.add(jRadioButton10);
    jRadioButton10.setText("Line");
    jRadioButton10.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jRadioButton10ActionPerformed(evt);
        }
    });

    jSlider2.setMajorTickSpacing(10);
    jSlider2.setMaximum(51);
    jSlider2.setMinimum(1);
    jSlider2.setMinorTickSpacing(5);
    jSlider2.setPaintTicks(true);
    jSlider2.addChangeListener(new javax.swing.event.ChangeListener() {
        public void stateChanged(javax.swing.event.ChangeEvent evt) {
            jSlider2StateChanged(evt);
        }
    });

    jLabel1.setText("Stroke Size (Radius)");

    javax.swing.GroupLayout jPanel4Layout = new javax.swing.GroupLayout(jPanel4);
    jPanel4.setLayout(jPanel4Layout);
    jPanel4Layout.setHorizontalGroup(
        jPanel4Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(jPanel4Layout.createSequentialGroup()
            .addContainerGap()
            .addGroup(jPanel4Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(jRadioButton9)
                .addComponent(jRadioButton10))
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 51, Short.MAX_VALUE)
            .addGroup(jPanel4Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
                .addComponent(jLabel1)
                .addComponent(jSlider2, javax.swing.GroupLayout.PREFERRED_SIZE, 150, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addContainerGap())
    );
    jPanel4Layout.setVerticalGroup(
        jPanel4Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(jPanel4Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
            .addComponent(jSlider2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGroup(jPanel4Layout.createSequentialGroup()
                .addGroup(jPanel4Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jRadioButton9)
                    .addComponent(jLabel1))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(jRadioButton10)))
    );

    jPanel2.setBackground(new java.awt.Color(255, 255, 255));
    jPanel2.setBorder(javax.swing.BorderFactory.createBevelBorder(javax.swing.border.BevelBorder.RAISED));
    jPanel2.addMouseListener(new java.awt.event.MouseAdapter() {
        public void mousePressed(java.awt.event.MouseEvent evt) {
            jPanel2MousePressed(evt);
        }
        public void mouseReleased(java.awt.event.MouseEvent evt) {
            jPanel2MouseReleased(evt);
        }
    });
    jPanel2.addMouseMotionListener(new java.awt.event.MouseMotionAdapter() {
        public void mouseDragged(java.awt.event.MouseEvent evt) {
            jPanel2MouseDragged(evt);
        }
    });

    javax.swing.GroupLayout jPanel2Layout = new javax.swing.GroupLayout(jPanel2);
    jPanel2.setLayout(jPanel2Layout);
    jPanel2Layout.setHorizontalGroup(
        jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 596, Short.MAX_VALUE)
    );
    jPanel2Layout.setVerticalGroup(
        jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 357, Short.MAX_VALUE)
    );

    jPanel3.setBorder(javax.swing.BorderFactory.createTitledBorder("Color"));

    buttonGroup2.add(jRadioButton3);
    jRadioButton3.setText("Red");
    jRadioButton3.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jRadioButton3ActionPerformed(evt);
        }
    });

    buttonGroup2.add(jRadioButton4);
    jRadioButton4.setText("Black");
    jRadioButton4.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jRadioButton4ActionPerformed(evt);
        }
    });

    buttonGroup2.add(jRadioButton5);
    jRadioButton5.setText("Gray");
    jRadioButton5.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jRadioButton5ActionPerformed(evt);
        }
    });

    buttonGroup2.add(jRadioButton6);
    jRadioButton6.setText("Green");
    jRadioButton6.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jRadioButton6ActionPerformed(evt);
        }
    });

    buttonGroup2.add(jRadioButton7);
    jRadioButton7.setText("White");
    jRadioButton7.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jRadioButton7ActionPerformed(evt);
        }
    });

    buttonGroup2.add(jRadioButton8);
    jRadioButton8.setText("Blue");
    jRadioButton8.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jRadioButton8ActionPerformed(evt);
        }
    });

    javax.swing.GroupLayout jPanel3Layout = new javax.swing.GroupLayout(jPanel3);
    jPanel3.setLayout(jPanel3Layout);
    jPanel3Layout.setHorizontalGroup(
        jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(jPanel3Layout.createSequentialGroup()
            .addContainerGap()
            .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                .addComponent(jRadioButton3, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(jRadioButton4, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, 66, Short.MAX_VALUE))
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(jRadioButton5, javax.swing.GroupLayout.DEFAULT_SIZE, 55, Short.MAX_VALUE)
                .addComponent(jRadioButton6, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
                .addComponent(jRadioButton8, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(jRadioButton7, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
            .addContainerGap())
    );
    jPanel3Layout.setVerticalGroup(
        jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel3Layout.createSequentialGroup()
            .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(jRadioButton4)
                .addComponent(jRadioButton5)
                .addComponent(jRadioButton7))
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 3, Short.MAX_VALUE)
            .addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(jRadioButton3)
                .addComponent(jRadioButton6)
                .addComponent(jRadioButton8)))
    );

    jButton1.setText("Clear");
    jButton1.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jButton1ActionPerformed(evt);
        }
    });

    jButton2.setText("About");
    jButton2.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jButton2ActionPerformed(evt);
        }
    });

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(jPanel2, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addGroup(layout.createSequentialGroup()
                    .addComponent(jPanel4, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                    .addComponent(jPanel3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                        .addComponent(jButton2, javax.swing.GroupLayout.DEFAULT_SIZE, 112, Short.MAX_VALUE)
                        .addComponent(jButton1, javax.swing.GroupLayout.DEFAULT_SIZE, 112, Short.MAX_VALUE))))
            .addContainerGap())
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                .addGroup(layout.createSequentialGroup()
                    .addGap(4, 4, 4)
                    .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 30, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                    .addComponent(jButton2, javax.swing.GroupLayout.PREFERRED_SIZE, 28, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addComponent(jPanel4, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(jPanel3, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(jPanel2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
            .addContainerGap())
    );

    pack();
}// </editor-fold>                        

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    System.out.println("You cleared the canvas.");
}                                        

private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                         

    JOptionPane.showMessageDialog(null, "JavaPaint is a simple java based painting application."
            + "  Nick R 5/22/2011", "About", JOptionPane.INFORMATION_MESSAGE);
}                                        
int currentX, currentY, oldX, oldY;

private void jPanel2MouseDragged(java.awt.event.MouseEvent evt) {                                     
    currentX = evt.getX();
    currentY = evt.getY();
    repaint();
    if (tool == 1) {
        oldX = currentX;
        oldY = currentY;
        System.out.println("Using pen at " + currentX + ", " + currentY);
    }

}                                    

private void jPanel2MousePressed(java.awt.event.MouseEvent evt) {                                     

    oldX = evt.getX();
    oldY = evt.getY();
    if (tool == 2) {
        currentX = oldX;
        currentY = oldY;
    } 


}                                    
//Tool Selection//
int tool = 0;
private void jRadioButton9ActionPerformed(java.awt.event.ActionEvent evt) {                                              
    tool = 1;
    System.out.println("Using the pen tool.");
}                                             

private void jRadioButton10ActionPerformed(java.awt.event.ActionEvent evt) {                                               
    tool = 2;
    System.out.println("Using the line tool.");
}                                              
//Slider Properties//
double value = 5;
private void jSlider2StateChanged(javax.swing.event.ChangeEvent evt) {                                      
    value = jSlider2.getValue();
    System.out.println(value);
}                                     
//COLOR CODE//
int color = 1;
private void jRadioButton4ActionPerformed(java.awt.event.ActionEvent evt) {                                              
    color = 1;        // Black
}                                             

private void jRadioButton5ActionPerformed(java.awt.event.ActionEvent evt) {                                              
    color = 2;        // Grey
}                                             

private void jRadioButton7ActionPerformed(java.awt.event.ActionEvent evt) {                                              
    color = 3;        // White
}                                             

private void jRadioButton3ActionPerformed(java.awt.event.ActionEvent evt) {                                              
    color = 4;    // Red
}                                             

private void jRadioButton6ActionPerformed(java.awt.event.ActionEvent evt) {                                              
    color = 5;        // Green
}                                             

private void jRadioButton8ActionPerformed(java.awt.event.ActionEvent evt) {                                              
    color = 6;        // Blue
}                                             

//mouse released//
private void jPanel2MouseReleased(java.awt.event.MouseEvent evt) {                                      

    currentX = evt.getX();
    currentY = evt.getY();
    if (tool == 2) {
        System.out.println("line from " + oldX +", "+ oldY + " to " + currentX + ", " + currentY);
    }
}                                     

//set ui visible//
public static void main(String args[]) {
    java.awt.EventQueue.invokeLater(new Runnable() {

        public void run() {
            new JavaPaintUI().setVisible(true);
        }
    });
}
// Variables declaration - do not modify                     
private javax.swing.ButtonGroup buttonGroup1;
private javax.swing.ButtonGroup buttonGroup2;
private javax.swing.JButton jButton1;
private javax.swing.JButton jButton2;
private javax.swing.JLabel jLabel1;
public javax.swing.JPanel jPanel2;
private javax.swing.JPanel jPanel3;
private javax.swing.JPanel jPanel4;
private javax.swing.JRadioButton jRadioButton10;
private javax.swing.JRadioButton jRadioButton3;
private javax.swing.JRadioButton jRadioButton4;
private javax.swing.JRadioButton jRadioButton5;
private javax.swing.JRadioButton jRadioButton6;
private javax.swing.JRadioButton jRadioButton7;
private javax.swing.JRadioButton jRadioButton8;
private javax.swing.JRadioButton jRadioButton9;
public javax.swing.JSlider jSlider2;
// End of variables declaration                   
class Panel2 extends JPanel {

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);

       if(color==1)
        g2.setPaint( Color.black );
        else if(color==2)
        g2.setPaint( Color.gray);
        else if(color==3)
        g2.setPaint( Color.white );
        else if(color==4)
        g2.setPaint( Color.red );
        else if(color==5)
        g2.setPaint( Color.green );
        else if(color==6)
        g2.setPaint( Color.blue );

        if (tool == 1) {

            g2.fillOval(currentX - ((int) value / 2), currentY - ((int) value / 2), (int) value, (int) value);
        } else if (tool == 2) {
            g2.setStroke(new BasicStroke((float) value, BasicStroke.CAP_ROUND,BasicStroke.JOIN_ROUND));
            g2.drawLine(oldX, oldY, currentX, currentY);
            g2.setStroke(new BasicStroke(1.0f));
        }


    }
}
}

Thanks ahead!

Andrew Thompson
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Nick R
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  • Why not post an [SSCCE](http://pscode.org/sscce.html) we can play with? How did you go with camickr's example linked from your last(?) question? Did you look at HFOE's example? – Andrew Thompson May 26 '11 at 02:32
  • well i see that they use arrays to store the color info and such. do i do the actual painting (drawline...) inside the jpanel class or inside my main class with the events in it(what i recently tried/edited) ima ima try to make a sscce real quick. Should i make it with the format i tried above or before? cause im pretty sure i did the whole image thing wrong – Nick R May 26 '11 at 03:07
  • wana just send it back to me working? ;) haha. the thing is when i try to adapt others examples it doesnt work and i have no idea what to do to fix it. Ignoring line color and line width, can you explain to me what exactly i need to do in relevance to my script( the structure is whats messing with me)? – Nick R May 26 '11 at 03:21
  • Where was the NullPointerException? Source filename and line number. BTW, it's better to pass in the graphics2D variable from paintComponent() into clear() instead of making it a field and call graphics2D.dispose() in paintComponent after clear() returns. This way references to graphics2D are only possible during the paintComponent. – karmakaze May 26 '11 at 03:21
  • one moment karmakaze i deleted that attempt at it. i don't get how i call upon the graphics2D from how my events are set up, like where i put the (g.drawLine(x1,y1,x2,y2);. – Nick R May 26 '11 at 03:26
  • Just a side note - Processing is much more suited for these kinds of tasks http://processing.org/ – Denis Tulskiy May 26 '11 at 03:31
  • ^ probably much more simple to make this than java haha. cool, but the class this is due in is java :( – Nick R May 26 '11 at 03:43

2 Answers2

7

OK - here are a ..few changes. 

import java.awt.*;
import java.awt.image.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import javax.swing.event.*;

public class JavaPaintUI extends JFrame {

    private BufferedImage canvas;

/** Creates new form JavaPaintUI */
public JavaPaintUI() {
    initComponents();
}

    //this was moved from the overriden paintComponent()
    // instead it update the canvas BufferedImage and calls repaint()
    public void updateCanvas() {
        Graphics2D g2d = canvas.createGraphics();
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);

        g2d.setPaint( getColor() );

        if (tool == 1) {

            g2d.fillOval(currentX - ((int) value / 2), currentY - ((int) value / 2), (int) value, (int) value);
        } else if (tool == 2) {
            g2d.setStroke(new BasicStroke((float) value, BasicStroke.CAP_ROUND,BasicStroke.JOIN_ROUND));
            g2d.drawLine(oldX, oldY, currentX, currentY);
            g2d.setStroke(new BasicStroke(1.0f));
        }
        repaint();
    }

    // used in both the updateCanvas and 'clear' method.
    private Color getColor() {
        Color c = null;
       if(color==1)
        c = Color.black;
        else if(color==2)
        c = Color.gray;
        else if(color==3)
        c = Color.white;
        else if(color==4)
        c = Color.red;
        else if(color==5)
        c = Color.green;
        else if(color==6)
        c = Color.blue;

        return c;
    }

// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {

    canvas = new BufferedImage(600,400,BufferedImage.TYPE_INT_RGB);

    buttonGroup1 = new ButtonGroup();
    buttonGroup2 = new ButtonGroup();
    jPanel4 = new JPanel();
    jRadioButton9 = new JRadioButton();
    jRadioButton10 = new JRadioButton();
    jSlider2 = new JSlider();
    jLabel1 = new JLabel();
    jPanel2 = new JPanel(new GridBagLayout());
    JLabel canvasLabel = new JLabel(new ImageIcon(canvas));
    jPanel2.add(canvasLabel, null);

    jPanel3 = new JPanel();
    jRadioButton3 = new JRadioButton();
    jRadioButton4 = new JRadioButton();
    jRadioButton5 = new JRadioButton();
    jRadioButton6 = new JRadioButton();
    jRadioButton7 = new JRadioButton();
    jRadioButton8 = new JRadioButton();
    jButton1 = new JButton();
    jButton2 = new JButton();

    setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    setTitle("JavaPaint ~ Nick R");

    jPanel4.setBorder(BorderFactory.createTitledBorder("Tool"));

    buttonGroup1.add(jRadioButton9);
    jRadioButton9.setText("Pen");
    jRadioButton9.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            jRadioButton9ActionPerformed(evt);
        }
    });

    buttonGroup1.add(jRadioButton10);
    jRadioButton10.setText("Line");
    jRadioButton10.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            jRadioButton10ActionPerformed(evt);
        }
    });

    jSlider2.setMajorTickSpacing(10);
    jSlider2.setMaximum(51);
    jSlider2.setMinimum(1);
    jSlider2.setMinorTickSpacing(5);
    jSlider2.setPaintTicks(true);
    jSlider2.addChangeListener(new ChangeListener() {
        public void stateChanged(ChangeEvent evt) {
            jSlider2StateChanged(evt);
        }
    });

    jLabel1.setText("Stroke Size (Radius)");

    GroupLayout jPanel4Layout = new GroupLayout(jPanel4);
    jPanel4.setLayout(jPanel4Layout);
    jPanel4Layout.setHorizontalGroup(
        jPanel4Layout.createParallelGroup(GroupLayout.Alignment.LEADING)
        .addGroup(jPanel4Layout.createSequentialGroup()
            .addContainerGap()
            .addGroup(jPanel4Layout.createParallelGroup(GroupLayout.Alignment.LEADING)
                .addComponent(jRadioButton9)
                .addComponent(jRadioButton10))
            .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED, 51, Short.MAX_VALUE)
            .addGroup(jPanel4Layout.createParallelGroup(GroupLayout.Alignment.TRAILING)
                .addComponent(jLabel1)
                .addComponent(jSlider2, GroupLayout.PREFERRED_SIZE, 150, GroupLayout.PREFERRED_SIZE))
            .addContainerGap())
    );
    jPanel4Layout.setVerticalGroup(
        jPanel4Layout.createParallelGroup(GroupLayout.Alignment.LEADING)
        .addGroup(jPanel4Layout.createParallelGroup(GroupLayout.Alignment.TRAILING)
            .addComponent(jSlider2, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)
            .addGroup(jPanel4Layout.createSequentialGroup()
                .addGroup(jPanel4Layout.createParallelGroup(GroupLayout.Alignment.BASELINE)
                    .addComponent(jRadioButton9)
                    .addComponent(jLabel1))
                .addPreferredGap(LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(jRadioButton10)))
    );

    jPanel2.setBackground(new Color(128, 40, 128));
    jPanel2.setBorder(BorderFactory.createBevelBorder(BevelBorder.RAISED));
    // add the listeners to the label that contains the canvas buffered image
    canvasLabel.addMouseListener(new MouseAdapter() {
        public void mousePressed(MouseEvent evt) {
            jPanel2MousePressed(evt);
        }
        public void mouseReleased(MouseEvent evt) {
            jPanel2MouseReleased(evt);
        }
    });
    canvasLabel.addMouseMotionListener(new MouseMotionAdapter() {
        public void mouseDragged(MouseEvent evt) {
            jPanel2MouseDragged(evt);
        }
    });

    // this part of the code was not helping.
    // either layout a container or custom paint it.
    // only attempt both if you are very confident of what you are doing.
/*
    GroupLayout jPanel2Layout = new GroupLayout(jPanel2);
    jPanel2.setLayout(jPanel2Layout);
    jPanel2Layout.setHorizontalGroup(
        jPanel2Layout.createParallelGroup(GroupLayout.Alignment.LEADING)
        .addGap(0, 596, Short.MAX_VALUE)
    );
    jPanel2Layout.setVerticalGroup(
        jPanel2Layout.createParallelGroup(GroupLayout.Alignment.LEADING)
        .addGap(0, 357, Short.MAX_VALUE)
    );
*/
    jPanel3.setBorder(BorderFactory.createTitledBorder("Color"));

    buttonGroup2.add(jRadioButton3);
    jRadioButton3.setText("Red");
    jRadioButton3.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            jRadioButton3ActionPerformed(evt);
        }
    });

    buttonGroup2.add(jRadioButton4);
    jRadioButton4.setText("Black");
    jRadioButton4.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            jRadioButton4ActionPerformed(evt);
        }
    });

    buttonGroup2.add(jRadioButton5);
    jRadioButton5.setText("Gray");
    jRadioButton5.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            jRadioButton5ActionPerformed(evt);
        }
    });

    buttonGroup2.add(jRadioButton6);
    jRadioButton6.setText("Green");
    jRadioButton6.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            jRadioButton6ActionPerformed(evt);
        }
    });

    buttonGroup2.add(jRadioButton7);
    jRadioButton7.setText("White");
    jRadioButton7.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            jRadioButton7ActionPerformed(evt);
        }
    });

    buttonGroup2.add(jRadioButton8);
    jRadioButton8.setText("Blue");
    jRadioButton8.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            jRadioButton8ActionPerformed(evt);
        }
    });

    GroupLayout jPanel3Layout = new GroupLayout(jPanel3);
    jPanel3.setLayout(jPanel3Layout);
    jPanel3Layout.setHorizontalGroup(
        jPanel3Layout.createParallelGroup(GroupLayout.Alignment.LEADING)
        .addGroup(jPanel3Layout.createSequentialGroup()
            .addContainerGap()
            .addGroup(jPanel3Layout.createParallelGroup(GroupLayout.Alignment.LEADING, false)
                .addComponent(jRadioButton3, GroupLayout.Alignment.TRAILING, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(jRadioButton4, GroupLayout.Alignment.TRAILING, GroupLayout.DEFAULT_SIZE, 66, Short.MAX_VALUE))
            .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED)
            .addGroup(jPanel3Layout.createParallelGroup(GroupLayout.Alignment.LEADING)
                .addComponent(jRadioButton5, GroupLayout.DEFAULT_SIZE, 55, Short.MAX_VALUE)
                .addComponent(jRadioButton6, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
            .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED)
            .addGroup(jPanel3Layout.createParallelGroup(GroupLayout.Alignment.TRAILING, false)
                .addComponent(jRadioButton8, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(jRadioButton7, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
            .addContainerGap())
    );
    jPanel3Layout.setVerticalGroup(
        jPanel3Layout.createParallelGroup(GroupLayout.Alignment.LEADING)
        .addGroup(GroupLayout.Alignment.TRAILING, jPanel3Layout.createSequentialGroup()
            .addGroup(jPanel3Layout.createParallelGroup(GroupLayout.Alignment.BASELINE)
                .addComponent(jRadioButton4)
                .addComponent(jRadioButton5)
                .addComponent(jRadioButton7))
            .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED, 3, Short.MAX_VALUE)
            .addGroup(jPanel3Layout.createParallelGroup(GroupLayout.Alignment.BASELINE)
                .addComponent(jRadioButton3)
                .addComponent(jRadioButton6)
                .addComponent(jRadioButton8)))
    );

    jButton1.setText("Clear");
    jButton1.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            jButton1ActionPerformed(evt);
        }
    });

    jButton2.setText("About");
    jButton2.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            jButton2ActionPerformed(evt);
        }
    });

    GroupLayout layout = new GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING)
                .addComponent(jPanel2, GroupLayout.Alignment.TRAILING, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addGroup(layout.createSequentialGroup()
                    .addComponent(jPanel4, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)
                    .addPreferredGap(LayoutStyle.ComponentPlacement.UNRELATED)
                    .addComponent(jPanel3, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)
                    .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED)
                    .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING)
                        .addComponent(jButton2, GroupLayout.DEFAULT_SIZE, 112, Short.MAX_VALUE)
                        .addComponent(jButton1, GroupLayout.DEFAULT_SIZE, 112, Short.MAX_VALUE))))
            .addContainerGap())
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING, false)
                .addGroup(layout.createSequentialGroup()
                    .addGap(4, 4, 4)
                    .addComponent(jButton1, GroupLayout.PREFERRED_SIZE, 30, GroupLayout.PREFERRED_SIZE)
                    .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED)
                    .addComponent(jButton2, GroupLayout.PREFERRED_SIZE, 28, GroupLayout.PREFERRED_SIZE))
                .addComponent(jPanel4, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(jPanel3, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
            .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(jPanel2, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
            .addContainerGap())
    );

    pack();
}// </editor-fold>

// clear the canvas using the currently selected color.
private void jButton1ActionPerformed(ActionEvent evt) {
    System.out.println("You cleared the canvas.");
    Graphics g = canvas.getGraphics();    
    g.setColor( getColor() );
    g.fillRect(0,0,canvas.getWidth(),canvas.getHeight());
    repaint();
}

private void jButton2ActionPerformed(ActionEvent evt) {

    JOptionPane.showMessageDialog(null, "JavaPaint is a simple java based painting application."
            + "  Nick R 5/22/2011", "About", JOptionPane.INFORMATION_MESSAGE);
}
int currentX, currentY, oldX, oldY;

private void jPanel2MouseDragged(MouseEvent evt) {
    currentX = evt.getX();
    currentY = evt.getY();
    updateCanvas();
    if (tool == 1) {
        oldX = currentX;
        oldY = currentY;
        System.out.println("Using pen at " + currentX + ", " + currentY);
    }

}

private void jPanel2MousePressed(MouseEvent evt) {

    oldX = evt.getX();
    oldY = evt.getY();
    if (tool == 2) {
        currentX = oldX;
        currentY = oldY;
    }


}
//Tool Selection//
int tool = 0;
private void jRadioButton9ActionPerformed(ActionEvent evt) {
    tool = 1;
    System.out.println("Using the pen tool.");
}

private void jRadioButton10ActionPerformed(ActionEvent evt) {
    tool = 2;
    System.out.println("Using the line tool.");
}
//Slider Properties//
double value = 5;
private void jSlider2StateChanged(ChangeEvent evt) {
    value = jSlider2.getValue();
    System.out.println(value);
}
//COLOR CODE//
int color = 1;
private void jRadioButton4ActionPerformed(ActionEvent evt) {
    color = 1;        // Black
}

private void jRadioButton5ActionPerformed(ActionEvent evt) {
    color = 2;        // Grey
}

private void jRadioButton7ActionPerformed(ActionEvent evt) {
    color = 3;        // White
}

private void jRadioButton3ActionPerformed(ActionEvent evt) {
    color = 4;    // Red
}

private void jRadioButton6ActionPerformed(ActionEvent evt) {
    color = 5;        // Green
}

private void jRadioButton8ActionPerformed(ActionEvent evt) {
    color = 6;        // Blue
}

//mouse released//
private void jPanel2MouseReleased(MouseEvent evt) {

    currentX = evt.getX();
    currentY = evt.getY();
    if (tool == 2) {
        System.out.println("line from " + oldX +", "+ oldY + " to " + currentX + ", " + currentY);
    }
}

//set ui visible//
public static void main(String args[]) {
    EventQueue.invokeLater(new Runnable() {

        public void run() {
            new JavaPaintUI().setVisible(true);
        }
    });
}
// Variables declaration - do not modify
private ButtonGroup buttonGroup1;
private ButtonGroup buttonGroup2;
private JButton jButton1;
private JButton jButton2;
private JLabel jLabel1;
public JPanel jPanel2;
private JPanel jPanel3;
private JPanel jPanel4;
private JRadioButton jRadioButton10;
private JRadioButton jRadioButton3;
private JRadioButton jRadioButton4;
private JRadioButton jRadioButton5;
private JRadioButton jRadioButton6;
private JRadioButton jRadioButton7;
private JRadioButton jRadioButton8;
private JRadioButton jRadioButton9;
public JSlider jSlider2;
// End of variables declaration
}

Screen shot

enter image description here

Community
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Andrew Thompson
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    cannot find symbol in canvas.addMouseListener(new MouseAdapter() {... and canvas.addMouseMotionListener(new MouseMotionAdapter() {... method addMouseListener(anonymous java.awt.event.MouseAdapter/MouseMotionAdapter) location: class java.awt.image.BufferedImage :-) – mKorbel May 26 '11 at 08:18
  • @mKorbel: My bad - it should have been added to the `canvasLabel`. Answer edited. – Andrew Thompson May 26 '11 at 09:00
3

Drawing into a buffer is just like drawing in a paintComponent(Graphics g). The difference is that you:

1) first create the buffer from any component (e.g. a Panel):

Image image = panel.createImage(width, height);

2) get the graphics context for the image:

Graphics g = image.getGraphics();

3) finally when done drawing into the buffer:

g.dispose();

Later, to draw the image onto your component:

void paintComponent(Graphics g) {
  g.drawImage(image, x_offset, y_offset, null);
}
karmakaze
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  • i attempted to do this (edited main post) but i achieved little success, any idea why? – Nick R May 26 '11 at 02:58
  • if i drawimage in paint component, where do i create and get the image (1 and 2) – Nick R May 26 '11 at 03:31
  • Once you have created your Panel2 instance, you can call panel2.createImage(w, h) on it to make the Image. When you want to draw do g = image.getGraphics(); drawing stuff; g.dispose(); – karmakaze May 26 '11 at 15:13