Extends JComponent to create drawing pad : JComponent « Swing « Java Tutorial

1. Java Tutorial
2. Swing
3. JComponent

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;

import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;

public class Main {
  public static void main(String[] args) {
    JFrame frame = new JFrame();
    final DrawPad drawPad = new DrawPad();
    frame.add(drawPad, BorderLayout.CENTER);
    JButton clearButton = new JButton("Clear");
    clearButton.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        drawPad.clear();
      }
    });
    frame.add(clearButton, BorderLayout.SOUTH);
    frame.setSize(280, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
  }

}
class DrawPad extends JComponent {
  Image image;
  Graphics2D graphics2D;
  int currentX, currentY, oldX, oldY;
  public DrawPad() {
    setDoubleBuffered(false);
    addMouseListener(new MouseAdapter() {
      public void mousePressed(MouseEvent e) {
        oldX = e.getX();
        oldY = e.getY();
      }
    });
    addMouseMotionListener(new MouseMotionAdapter() {
      public void mouseDragged(MouseEvent e) {
        currentX = e.getX();
        currentY = e.getY();
        if (graphics2D != null)
          graphics2D.drawLine(oldX, oldY, currentX, currentY);
        repaint();
        oldX = currentX;
        oldY = currentY;
      }
    });
  }

  public void paintComponent(Graphics g) {
    if (image == null) {
      image = createImage(getSize().width, getSize().height);
      graphics2D = (Graphics2D) image.getGraphics();
      graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
          RenderingHints.VALUE_ANTIALIAS_ON);
      clear();
    }
    g.drawImage(image, 0, 0, null);
  }

  public void clear() {
    graphics2D.setPaint(Color.white);
    graphics2D.fillRect(0, 0, getSize().width, getSize().height);
    graphics2D.setPaint(Color.black);
    repaint();
  }
}

14.2.JComponent
	14.2.1.	JComponent
	14.2.2.	HTML formatting by setting the text on a label
	14.2.3.	Listening to Inherited Events of a JComponent from Container and Component
	14.2.4.	Painting JComponent Objects
	14.2.5.	how an icon is adapted to a component
	14.2.6.	A Swing component that computes and displays a fractal image known as a 'Julia set'
	14.2.7.	Extends JComponent to create drawing pad
	14.2.8.	A panel that displays a paint sample.