SQL & PL/SQL

here ya go... there is a huge performance trick called double buffering.

Notice how each time we need to re-draw the polygon, we only draw to the buffered image instead of directly on the passed-in graphics argument? Thats the trick.

It avoid doing any geometry/java2d work in the majority of painting requests and instead painting is usualy only a simple copy-buffer operation.

import java.awt.AlphaComposite;
import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Polygon;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.image.BufferedImage;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Dragtest extends JFrame {

  boolean blPaintRect = false;
  Polygon d = new Polygon();
  Point srcPoint = null;
  Point destPoint = null;
  boolean blchecked;
  AlphaComposite alcomp = AlphaComposite.getInstance(
      AlphaComposite.SRC_OVER,
      0.4f);
  BufferedImage buffer;
  boolean dirty = true;

  JPanel canvas;

  public Dragtest() {
    
    canvas = new JPanel() {

      public void paintComponent(Graphics g) {

        if (dirty) {
          buffer = getUpdatedImage(canvas);
          Graphics2D bufferGraphics = (Graphics2D) buffer.getGraphics();
          super.paintComponent(bufferGraphics);

          if (blPaintRect) {
            bufferGraphics.setComposite(alcomp);
            // One optimisation is that ,
            // drawPolygon  be skipped , and only fillPolygon can be used 
            bufferGraphics.drawPolygon(d);
            bufferGraphics.fillPolygon(d);
          }
          dirty = false;
        }

        g.drawImage(buffer, 0, 0, getWidth(), getHeight(), this);
      }
    };

    canvas.addMouseMotionListener(new MouseMotionAdapter() {
      public void mouseDragged(MouseEvent e) {
        // blPaintRect is made true and repaint is called , to draw the box
        blPaintRect = true;
        Point p = e.getPoint();
       // p = SwingUtilities.convertPoint(Dragtest.this, p, canvas);
        if (srcPoint == null) {
          srcPoint = new Point(p.x, p.y);
          destPoint = srcPoint;
        } else {
          destPoint = new Point(p.x, p.y);
        }
        // As the user drags the mouse , the new co-ordinates are stored
        // in destPoint variable and the intial point in
        // srcPoint variable
        d.reset();
        d.addPoint(srcPoint.x, srcPoint.y);
        d.addPoint(destPoint.x, srcPoint.y);
        d.addPoint(destPoint.x, destPoint.y);
        d.addPoint(srcPoint.x, destPoint.y);
        dirty = true;
        repaint();
      }
    });

    canvas.addMouseListener(new MouseAdapter() {
      public void mouseReleased(MouseEvent e) {
        blPaintRect = false;
        srcPoint = null;
        dirty = true;
        repaint();
      }
    });

    canvas.setBorder(null);
    getContentPane().setLayout(new BorderLayout());
    getContentPane().add(canvas, BorderLayout.CENTER);
    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    pack();

    setSize(300, 300);
    setLocation(300, 100);
    setTitle("Java Speed Test");
    setVisible(true);
  }

  /**
   * @return a buffer same size as the given component.
   */
  private BufferedImage getUpdatedImage(Component c) {
    if (buffer == null) {
      buffer = new BufferedImage(1, 1, BufferedImage.TYPE_INT_BGR);
    } else {
      int bufferWidth = buffer.getWidth();
      int bufferHeight = buffer.getHeight();

      int componentWidth = c.getWidth();
      int componentHeight = c.getHeight();

      if (bufferWidth != componentWidth || bufferHeight != componentHeight) {
        buffer = new BufferedImage(
            componentWidth,
            componentHeight,
            BufferedImage.TYPE_INT_BGR);

      }
    }

    return buffer;
  }

  public static void main(String args[]) {
    new Dragtest().setVisible(true);
  }

}

Hmmm ... Thx for ur reply ..
I have a comment for ur code ..

1) The double buffering as u said as trick , which i dont think
rules here, because , evry time the component is painted when the mouse is presed , u have created a new graphics object in which u painted the polygon and displayed .

2) The Frame is the culprit here, Overriding the paint method of Frame is what making the fickering. When i tried my code (courtesy : your code !! ) with overriding a JPanel paint method , it works as smooth as possible .

import java.awt.event.MouseMotionAdapter;
import javax.swing.JLabel;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import java.awt.Point;
import java.awt.Graphics2D;
import java.awt.Polygon;
import java.awt.Graphics;
import java.awt.AlphaComposite;
import javax.swing.plaf.basic.BasicScrollPaneUI;
import javax.swing.JPanel;
import java.awt.BorderLayout;

public class DragTest2 extends JFrame{

    boolean blPaintRect = false;
    Polygon d = new Polygon();
    Point srcPoint = null;
    Point destPoint = null;
    boolean blchecked;
    AlphaComposite alcomp = AlphaComposite.getInstance(
                    AlphaComposite.SRC_OVER, 0.4f);
    JPanel myPanel;

    public DragTest2() {        
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        
        myPanel = new JPanel(){
            public void paint(Graphics g) {                
                if (blPaintRect) {
                    super.paint(g);
                    g.drawPolygon(d);
                    Graphics2D g2d = (Graphics2D) g;
                    g2d.setComposite(alcomp);
                    // One optimisation is that ,
                    // drawPolygon  be skipped , and only fillPolygon can be used
//                    g2d.drawPolygon(d);
                    g2d.fillPolygon(d);
                } else {
                    super.paint(g);
                }
            }
        };
        
        myPanel.addMouseMotionListener(new MouseMotionAdapter(){
            public void mouseDragged(MouseEvent e){
                // blPaintRect is made true and repaint is called , to draw the box
                blPaintRect = true;
                if(srcPoint == null){
                    srcPoint = e.getPoint();
                    destPoint = e.getPoint();
                }
                else{
                    destPoint = e.getPoint();
                }
                // As the user drags the mouse , the new co-ordinates are stored
                // in destPoint variable and the intial point in
                // srcPoint variable

                d.reset();
                d.addPoint(srcPoint.x, srcPoint.y);
                d.addPoint(destPoint.x, srcPoint.y);
                d.addPoint(destPoint.x, destPoint.y);
                d.addPoint(srcPoint.x, destPoint.y);

                myPanel.repaint();
            }
        } );

        myPanel.addMouseListener(new MouseAdapter(){
            public void mouseReleased(MouseEvent e) {
                blPaintRect = false;
                srcPoint = null;
                myPanel.repaint();
            }
        });
        
        add(myPanel, BorderLayout.CENTER);
        pack();

        setSize(300, 300);
        setLocation(300, 100);
        setTitle("Java Speed Test");
        setVisible(true);
    }

    public void paint2(Graphics g){
        if(blPaintRect){
            super.paint(g);
            Graphics2D  g2d = (Graphics2D) g;
            g2d.setComposite(alcomp);
            // One optimisation is that ,
            // drawPolygon  be skipped , and only fillPolygon can be used
            g2d.drawPolygon(d);
            g2d.fillPolygon(d);
        }
        else{
            super.paint(g);
        }
    }

    public static void main(String args[]) {
        new DragTest2().setVisible(true);
    }

}

Actually JVaudry overrode the paintComponent(...) method of JPanel, which is what you should be doing. In your particular example if probably won't make a difference, but overriding paint(..) is not the best approach. Read the [url http://java.sun.com/docs/books/tutorial/uiswing/14painting/concepts.html]Painting tutorial for more information.

yeah, i guess the main thing was to paint on the JPanel instead of the frame. The double buffering was not really needed.