问Java中的裸骨画家应用

EN

package net.coderodde.javapaint;

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.image.BufferedImage;

/**
 * This class implements a GUI component for drawing.
 * 
 * @author Rodion "rodde" Efremov
 * @version 1.6 (Jun 8, 2016)
 */
public class PaintCanvas extends Canvas {

    /**
     * The actual image being drawn to.
     */
    private final BufferedImage image;

    /**
     * The graphics context of the above.
     */
    private final Graphics2D imageGraphics;

    public PaintCanvas(final int width, final int height) {
        super();
        super.setBounds(0, 0, width, height);

        this.image  = new BufferedImage(width, 
                                        height, 
                                        BufferedImage.TYPE_INT_RGB);
        this.imageGraphics = this.image.createGraphics();
        this.imageGraphics.setColor(Color.WHITE);
        this.imageGraphics.fillRect(0, 0, width, height);
        this.imageGraphics.setColor(Color.BLACK);

        final PaintCanvasMouseListener listener =
                new PaintCanvasMouseListener();

        this.addMouseListener(listener);
        this.addMouseMotionListener(listener);
    }

    @Override
    public void paint(final Graphics g) {
        update(g);
    }

    @Override
    public void update(final Graphics g) {
        g.drawImage(this.image, 0, 0, null);
    }

    private class PaintCanvasMouseListener 
    extends MouseAdapter implements MouseMotionListener  {

        @Override
        public void mouseClicked(final MouseEvent event) {
            processEvent(event);
        }

        @Override
        public void mouseDragged(final MouseEvent event) {
            processEvent(event);
        }

        private void processEvent(final MouseEvent event) {
            PaintCanvas.this.imageGraphics.fillOval(event.getX(), event.getY(), 5, 5);
            PaintCanvas.this.repaint();
        }
    }
}

package net.coderodde.javapaint;

import java.awt.Dimension;
import java.awt.Toolkit;
import javax.swing.JFrame;

/**
 * This class implements an application for simple drawing.
 * 
 * @author Rodion "rodde" Efremov
 * @version 1.6 (Jun 8, 2016)
 */
public class App {

    private final JFrame frame = new JFrame("JavaPaint");

    public App() {
        frame.getContentPane().add(new PaintCanvas(640, 480));
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        setFrameLocationToCenter();
        frame.setVisible(true);
    }

    private void setFrameLocationToCenter() {
        final Dimension screenDimension = Toolkit.getDefaultToolkit()
                                                 .getScreenSize();
        final int screenWidth  = screenDimension.width;
        final int screenHeight = screenDimension.height;

        frame.setLocation((screenWidth - frame.getWidth()) / 2, 
                          (screenHeight - frame.getHeight()) / 2);
    }

    public static void main(final String... args) {
        final App app = new App();
    }
}