GridFiller Applet Write an applet that displays a 4 x 4 grid. When the user clicks on a square in the grid, the applet should draw a filled circle in it. If the square already has a circle, clicking on it should cause the circle to disappear. Solution import javax.swing.JApplet; import java.awt.Color; import java.awt.Graphics; import java.awt.event.MouseEvent; import java.awt.event.MouseListener; import javax.swing.JPanel; public class GridFiller extends JApplet { public void init() { GridFiller gridFiller = new GridFiller(); setContentPane(gridFiller); } class GridFiller extends JPanel implements MouseListener { int gridRow; int gridCol; GridFiller() { gridRow = -1; addMouseListener(this); } public void paintComponent(Graphics g) { int row; int col; int x,y; for (row=0; row<4; row++) { for (col=0; col<4; col++) { x = col * 50; y = col * 50; if ((row % 2) == (col % 2)) g.setColor(Color.blue); else g.setColor(Color.white); g.fillRect(x, y, 50, 50); } } if (gridRow >= 0) { g.setColor(Color.red); x = gridCol * 50; y = gridRow * 50; g.fillOval(x, y, 50, 50); } } public void mousePressed (MouseEvent evt) { int col = evt.getX() / 50; int row = evt.getY() / 50; if (gridRow == row && gridCol == col) gridRow = -1; else { gridRow = row; gridCol = col; } repaint(); } public void mouseReleased(MouseEvent evt){} public void mouseClicked(MouseEvent evt){} public void mouseEntered(MouseEvent evt){} public void mouseExited(MouseEvent evt){} } }.

1. GridFiller Applet
Write an applet that displays a 4 x 4 grid. When the user clicks on a square in the grid, the applet
should draw a filled circle in it. If the square already has a circle, clicking on it should cause the
circle to disappear.
Solution
import javax.swing.JApplet;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.JPanel;
public class GridFiller extends JApplet
{
public void init()
{
GridFiller gridFiller = new GridFiller();
setContentPane(gridFiller);
}
class GridFiller extends JPanel implements MouseListener
{
int gridRow;
int gridCol;
GridFiller()
{
gridRow = -1;
addMouseListener(this);
}
public void paintComponent(Graphics g)
{
int row;
int col;
int x,y;
for (row=0; row<4; row++)

2. {
for (col=0; col<4; col++)
{
x = col * 50;
y = col * 50;
if ((row % 2) == (col % 2))
g.setColor(Color.blue);
else
g.setColor(Color.white);
g.fillRect(x, y, 50, 50);
}
}
if (gridRow >= 0)
{
g.setColor(Color.red);
x = gridCol * 50;
y = gridRow * 50;
g.fillOval(x, y, 50, 50);
}
}
public void mousePressed (MouseEvent evt)
{
int col = evt.getX() / 50;
int row = evt.getY() / 50;
if (gridRow == row && gridCol == col)
gridRow = -1;
else
{
gridRow = row;
gridCol = col;
}
repaint();
}
public void mouseReleased(MouseEvent evt){}
public void mouseClicked(MouseEvent evt){}
public void mouseEntered(MouseEvent evt){}

3. public void mouseExited(MouseEvent evt){}
}
}