Java Tutorial/2D Graphics/Buffer Paint

Double buffer

import java.applet.Applet;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
public class DoubleBufferWithBufferedImage extends Applet {
  int gap = 3;
  int mx, my;
  Image buffer = null;
  int w, h;
  public static void main(String[] a) {
    JFrame f = new JFrame();
    f.setSize(300, 300);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.getContentPane().add(new DoubleBufferWithBufferedImage());
    f.setVisible(true);
  }
  public DoubleBufferWithBufferedImage() {
    setSize(300, 300);
    Dimension d = getSize();
    w = d.width;
    h = d.height;
    buffer = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
  }
  public void paint(Graphics g) {
    Graphics screengc = null;
    screengc = g;
    g = buffer.getGraphics();
    g.setColor(Color.blue);
    g.fillRect(0, 0, w, h);
    g.setColor(Color.red);
    for (int i = 0; i < w; i += gap)
      g.drawLine(i, 0, w - i, h);
    for (int i = 0; i < h; i += gap)
      g.drawLine(0, i, w, h - i);
    screengc.drawImage(buffer, 0, 0, null);
  }
}

Off Screen Paint: create Graphics from BufferedImage

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.Arc2D;
import java.awt.image.BufferedImage;
import javax.swing.JComponent;
import javax.swing.JFrame;
class MyCanvas extends JComponent {
  private BufferedImage offImg;
  public void draw(Graphics g) {
    Graphics2D g2 = (Graphics2D) g;
    // Draw the pie chart
    Arc2D.Float arc = new Arc2D.Float(Arc2D.PIE);
    arc.setFrame(140, 200, 67, 46);
    arc.setAngleStart(45);
    arc.setAngleExtent(270);
    g2.setColor(Color.gray);
    g2.draw(arc);
    g2.setColor(Color.red);
    g2.fill(arc);
    g2.setColor(Color.black);
    g2.drawString("Arc2D.PIE", 140, 190);
  }
  public Graphics2D createDemoGraphics2D(Graphics g) {
    Graphics2D g2 = null;
    if (offImg == null || offImg.getWidth() != getSize().width
        || offImg.getHeight() != getSize().height) {
      offImg = (BufferedImage) createImage(getSize().width, getSize().height);
    }
    if (offImg != null) {
      g2 = offImg.createGraphics();
      g2.setBackground(getBackground());
    }
    // .. set attributes ..
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
 
    // .. clear canvas ..
    g2.clearRect(0, 0, getSize().width, getSize().height);
    return g2;
  }
  public void paint(Graphics g) {
    if (getSize().width <= 0 || getSize().height <= 0)
      return;
    Graphics2D g2 = createDemoGraphics2D(g);
    draw(g2);
    g2.dispose();
    if (offImg != null && isShowing()) {
      g.drawImage(offImg, 0, 0, this);
    }
  }
}
public class OffScreenPaint {
  public static void main(String[] a) {
    JFrame window = new JFrame();
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setBounds(30, 30, 300, 300);
    window.getContentPane().add(new MyCanvas());
    window.setVisible(true);
  }
}