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

/*
 * Class - Java Paint - allows a user to paint on a panel
 */
public class JavaPaint extends JPanel implements ActionListener, ItemListener {        

    //color of brush
    private Color brushColor;
    //background color of paint panel
    private Color backgroundColor;
    //size of brush
    private int brushSize = 6;
    
    JLabel brushSizeLabel;
    JComboBox brushSizeCombo;
    JButton selectColor;
    
    //constructor - create instance of Java Paint    
    public JavaPaint() {    
        //set border layout
        super(new BorderLayout());
        //create GUI
        createGUI();
    }

    //entry point of the application
    public static void main(String[] args) {
        //create main frame with title "Java Paint"
        JFrame frame = new JFrame("Java Paint");                
        
        //add main Panel to frame
        frame.add(new JavaPaint());
        
        //configure frame
        //exit when user clicks close
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //disable resize
        frame.setResizable(false);
        //set preferred size
        frame.setPreferredSize(new Dimension(500, 550));
        frame.pack();       
        //set location of the frame to center
        frame.setLocationRelativeTo(null);
        //show frame
        frame.setVisible(true);
    }

    //creat GUI - components
    private void createGUI() {    
        //create paint panel
        PaintPanel paintPanel = new PaintPanel();
        //get background color of paintPanel
        backgroundColor = paintPanel.getBackground();
        //add paintPanel to the main panel
        this.add(paintPanel, BorderLayout.CENTER);
        
        //create bottom(control) panel
        JPanel bottomPanel = new JPanel();
        //change color of the panel
        bottomPanel.setBackground(Color.LIGHT_GRAY);
        //set border to panel (for alignment)
        bottomPanel.setBorder(BorderFactory.createEmptyBorder(20, 0, 20, 0));
        
        //create label
        brushSizeLabel = new JLabel("Set the brush size: ");
        //add label to bottom panel
        bottomPanel.add(brushSizeLabel);
        
        //create combobox for brush size
        brushSizeCombo = new JComboBox();
        //disable editing
        brushSizeCombo.setEditable(false);
        //loop through 1 to 10
        for (int i=1; i<11; i++) {
            //add item to combobox ("1", "2", "3" and so on... )
            brushSizeCombo.addItem(String.valueOf(i));
        }
        //choose default item for combobox
        brushSizeCombo.setSelectedIndex(4);
        //add item listener (to listen for changes)
        brushSizeCombo.addItemListener(this);
        //add combobox to bottom panel
        bottomPanel.add(brushSizeCombo);
        
        //create empty area between combobox and button
        bottomPanel.add(Box.createRigidArea(new Dimension(50, 0)));
        
        //create button for selecting color
        selectColor = new JButton("Select Paint Color");
        //add action listener
        selectColor.addActionListener(this);
        //add button to bottom panel
        bottomPanel.add(selectColor);
        
        //add bottom panel to main panel
        this.add(bottomPanel, BorderLayout.PAGE_END);
    }
    
    //class - panel for painting
    private class PaintPanel extends JPanel implements MouseMotionListener {
        //image for buffering and saving picture
        Image bufferImage;
        //graphic to draw
        Graphics backgroundGraphics;
        
        //constructor of PainPanel
        public PaintPanel() {
            //set sizes of the panel
            this.setPreferredSize(new Dimension(500, 400));
            this.setSize(new Dimension(500, 400));
            
            //add mouse motion listener to listen for dragging
            this.addMouseMotionListener(this);

        }
        
        //we don't need this method
        //write it 'cause we implement MouseMotionListener
        public void mouseMoved( MouseEvent e ) { }
        
        //run if user dragged mouse
        public void mouseDragged(MouseEvent e) {
         //get location of mouse
         int x = e.getX();
            int y = e.getY();
            //find if user clicked left or right button
            if (SwingUtilities.isLeftMouseButton(e)) {
             //if left - set color to bruseh - paint on panel
             backgroundGraphics.setColor(brushColor);
            }
            else {
             //if right - set color to background - erase from panel
             backgroundGraphics.setColor(backgroundColor);
            }
            
            //paint oval on buffered image
            backgroundGraphics.fillOval(x-brushSize/2,y-brushSize/2,brushSize,brushSize);
            
            //repaint panel
            repaint();
        }
        
        //create buffered image if it doesn't exist
        private void createBufferedImage() {
         Dimension d = getSize();
         //if no image - create it
         if (bufferImage == null) {
             bufferImage = createImage(d.width, d.height);
         }
        }
        
        //update panel by drawing buffered image on it
        public void update( Graphics g ) {
            g.drawImage( bufferImage, 0, 0, this );
        }

        //paint on panel
        public void paint( Graphics g ) {
            //create buffered image if it doesn't exist
            createBufferedImage();            
            //set background graphics to image graphics
            backgroundGraphics = bufferImage.getGraphics();    
            //update panel
            update(g);
        }
        
    }
    
    //user clicked select paint color button
    public void actionPerformed(ActionEvent e) {
        //show color dialog and get new color
        Color newColor = JColorChooser.showDialog(
                                       JavaPaint.this,
                                       "Select Paint Color",
                                       brushColor);
        //check if user selected new color
        if (newColor != null) {
         //set brush color to new
            brushColor = newColor;
        }
    }

    //user changed combobox
    public void itemStateChanged(ItemEvent e) {
        //check if user select item
        if (e.getStateChange() == ItemEvent.SELECTED) {
            //get selected item as string
            String newBrushSize = (String)e.getItem();
            //set brush size
            brushSize = Integer.parseInt(newBrushSize)+1;
        }
        
    }
}