Don't use these tips without understanding what happens !

To put an Image...

        bi = new BufferedImage[4];
        String s[] = { "bld.jpg", "bld.jpg", "boat.gif", "boat.gif"};
        for ( int i = 0; i < bi.length; i++ )	{
            Image img = getImage(getURL("images/" + s[i]));
            try	{
                MediaTracker tracker = new MediaTracker(this);
                tracker.addImage(img, 0);
                tracker.waitForID(0);
            }
            catch ( Exception e ) {}
            int iw = img.getWidth(this);
            int ih = img.getHeight(this);
            bi[i] = new BufferedImage(iw, ih, BufferedImage.TYPE_INT_RGB);
            Graphics2D big = bi[i].createGraphics();
            big.drawImage(img,0,0,this);
        }
 

To get the dimension of a bouding container

   addNotify();
   Insets insets = getInsets(); // from inside one container
   then you get ...
   insets.top
   insets.bottom
   insets.left
   insets.right

Recursion

solveRecursively(Problem p)	{
	if (p is trivial)	return(the obvious answer);

	// else simplify the problem
	Problem p1 = simplerProblem(p);

	s1 = solveRecursively(p1);
	
	// Turn the solution of simpler pb into solution of original problem
	s = solutionOfOriginalProblem(s1);
	return s1;
}

Careful

• Be always sure that simplerProblem will really bring you towards a trivial problem
• Be sure to always test for the case of trivial problem that will end the recursivity

To create a package...

To test the effectiveness of that procedure, you should try with a file that contains at least 2
Classes

• Chose a Package name (Sun advice is to use your reversed Internet domain name). E.g. : net.vuylsteker.test
• Put a Package statement in your file
  package net.vuylsteker.test
• Check that your CLASSPATH environment variable is well set
  It could be set in a .bashrc file for instance :
  CLASSPATH="$CLASSPATH;Z:\ClassDir"
export CLASSPATH
• Compile with an option that will put your class in the right hierarchy
  javac -d "Z:\ClassDir" HelloWord.java
• Test your package from another location, with the import statement
  import net.vuylsteker.test.*

To let a user chose a file

JFileChooser chooser = new JFileChooser(); 


int returnVal = chooser.showOpenDialog(this);
if(returnVal == JFileChooser.APPROVE_OPTION)	{ 
   fichier = chooser.getSelectedFile();
   System.out.println("You chose to open this file: " + fichier.getName());
   System.out.println("You chose to open this file: " + fichier.getAbsolutePath());
} 
 

To Do some Pick and Move

class ShowPanel extends JPanel implements MouseListener, MouseMotionListener	{ 
	ShowPanel(File f)	{
		addMouseMotionListener(this);
		addMouseListener(this);
		setBackground(Color.white);
			
		../..
	}


	// Handles the event of the user pressing down the mouse button.
    public void mousePressed(MouseEvent e)	{
		last_x = rect.x - e.getX();
		last_y = rect.y - e.getY();

		// Checks whether or not the cursor is inside of the rectangle
		// while the user is pressing the mouse.
		if ( rect.contains(e.getX(), e.getY()) )	{
			updateLocation(e);
		}	else	{
			System.out.println("First position the cursor on the rectangle and then drag.");
			pressOut = true;
		}
	}

    // Handles the event of a user dragging the mouse while holding
    // down the mouse button.
    public void mouseDragged(MouseEvent e)	{
		if ( !pressOut )	{
			updateLocation(e);
		} else	{
			System.out.println("First position the cursor on the rectangle and then drag.");
	    }
    }

    // Handles the event of a user releasing the mouse button.
    public void mouseReleased(MouseEvent e)	{
		// Checks whether or not the cursor is inside of the rectangle
		// when the user releases the mouse button.
		if ( rect.contains(e.getX(), e.getY()) )	{
			updateLocation(e);
		} else	{
			System.out.println("First position the cursor on the rectangle and then drag.");
			pressOut = false;
		}
    }
       
     // This method is required by MouseListener.
     public void mouseMoved(MouseEvent e)	{}
     // These methods are required by MouseMotionListener.
     public void mouseClicked(MouseEvent e)	{}
     public void mouseExited(MouseEvent e)	{}
     public void mouseEntered(MouseEvent e)	{}
                         
     // Updates the coordinates representing the location of the current rectangle.
     public void updateLocation(MouseEvent e)	{
		rect.setLocation(last_x + e.getX(), last_y + e.getY());
			/*
			 * Updates the label to reflect the location of the
			 * current rectangle
			 * if checkRect returns true; otherwise, returns error message.
			 */
			if (checkRect())	{
				System.out.println("Rectangle located at " + rect.getX() + ", " + rect.getY());
			} else	{
                    System.out.println("Please don't try to "+ " drag outside the area.");
			}
		repaint();
     }


	public void paintComponent(Graphics g)	{
		super.paintComponent(g);
		Graphics2D g2 = (Graphics2D) g;
		
		// Draws and fills the newly positioned rectangle.
        g2.setPaint(Color.red);
		g.drawString("Bonjour...  "+name, 20, 20);
		g.drawImage(img,rect.x,rect.y,null);
	}

eScience