Applets and More 5, GridFiller Applets Write an applet that displays a 4 X 4 gri

Question

Applets and More

5, GridFiller Applets

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.

9, Stopwatch Applet

Write an applet that simulates a stopwatch. It should have a Start button and a Stop button. When the Start is clicked the applet should count the seconds that pass. When the Stop button is clicked, the applet should stop counting seconds.

Explanation / Answer

import java.awt.*;

import java.applet.Applet;

import java.awt.event.*;

public class GridDrawingApplet extends Applet {

public void paint (Graphics g)

{

// Draw the vertical lines:

g.drawLine (0,0, 0,240);

g.drawLine (30,0, 30,240);

g.drawLine (60,0, 60,240);

g.drawLine (90,0, 90,240);

g.drawLine (120,0, 120,240);

g.drawLine (150,0, 150,240);

g.drawLine (180,0, 180,240);

g.drawLine (210,0, 210,240);

g.drawLine (240,0, 240,240);

  

// Draw the horizontal lines:

g.drawLine (0,0, 240,0);

g.drawLine (0,30, 240,30);

g.drawLine (0,60, 240,60);

g.drawLine (0,90, 240,90);

g.drawLine (0,120, 240,120);

g.drawLine (0,150, 240,150);

g.drawLine (0,180, 240,180);

g.drawLine (0,210, 240,210);

g.drawLine (0,240, 240,240);

}

}

Alternate way of drawing an applet

import java.awt.*;

import java.applet.Applet;

import java.awt.event.*;

public class GridDrawingAppletForLoop extends Applet {

public void paint (Graphics g)

{

// Draw the vertical lines:

for (int x=0; x<=240; x+=30) {

g.drawLine (x,0, x,240);

}

// Draw the horizontal lines:

for (int y=0; y<=240; y+=30) {

g.drawLine (0,y, 240,y);

}

}

}

import java.awt.*;

import java.awt.event.*;

import java.applet.Applet;

public class BouncingBallApplet2 extends Applet implements Runnable, MouseListener {

int delay;

int frameNumber;

Thread animatorThread;

public void init ()

{

delay = 500;

animatorThread = null;

// Need to tell Java to call "us" when a mouseclick occurs.

addMouseListener (this);

}

public void start ()

{

frameNumber = 0;

if (animatorThread == null) {

animatorThread = new Thread (this);

}

animatorThread.start ();

}

public void stop ()

{

animatorThread = null;

}

public void run ()

{

while (animatorThread != null) {

frameNumber ++;

// Draw next frame.

repaint ();

// Delay

try {

Thread.sleep (delay);

}

catch (InterruptedException e) {

break;

}

}

}

public void paint (Graphics g)

{

// Set foreground and background colors.

setBackground (Color.white);

g.setColor (Color.blue);

// Here's how to get the size of the applet bounds within the program:

// d.width is the width, d.height is the height.

Dimension d = getSize();

if (frameNumber % 2 == 1) {

// On odd frames, draw the ball at the top.

g.fillOval (0, 0, d.width/2, d.height/2);

}

else {

// On even frames, draw the ball at the bottom.

g.fillOval (0, d.height/2, d.width/2, d.height/2);

}

}

// This method gets called when mouse click occurs.

public void mouseClicked (MouseEvent e)

{

// Draw a small red dot where the click occurred.

int x = e.getX ();

int y = e.getY ();

Graphics g = getGraphics ();

g.setColor (Color.red);

g.fillOval (x-5, y-5, 10, 10);

// If no thread is running, we'll create one.

if (animatorThread == null) {

start ();

}

else {

stop ();

}

}

  

// We need to have these methods, but

// don't actually have to do anything inside.

public void mouseEntered (MouseEvent m) {}

public void mouseExited (MouseEvent m) {}

public void mousePressed (MouseEvent m) {}

public void mouseReleased (MouseEvent m) {}

}

9.import java.awt.event.*;

import javax.swing.*;

public class StopWatch extends JLabel

implements MouseListener, ActionListener {

private long startTime; // Start time of stopwatch.

// (Time is measured in milliseconds.)

private boolean running; // True when the stopwatch is running.

private Timer timer; // A timer that will generate events

// while the stopwatch is running

public StopWatch() {

// Constructor.

super(" Click to start timer. ", JLabel.CENTER);

addMouseListener(this);

}

public void actionPerformed(ActionEvent evt) {

// This will be called when an event from the

// timer is received. It just sets the stopwatch

// to show the amount of time that it has been running.

// Time is rounded down to the nearest second.

long time = (System.currentTimeMillis() - startTime) / 1000;

setText("Running: " + time + " seconds");

}

public void mousePressed(MouseEvent evt) {

// React when user presses the mouse by

// starting or stopping the stopwatch. Also start

// or stop the timer.

if (running == false) {

// Record the time and start the stopwatch.

running = true;

startTime = evt.getWhen(); // Time when mouse was clicked.

setText("Running: 0 seconds");

if (timer == null) {

timer = new Timer(100,this);

timer.start();

}

else

timer.restart();

}

else {

// Stop the stopwatch. Compute the elapsed time since the

// stopwatch was started and display it.

timer.stop();

running = false;

long endTime = evt.getWhen();

double seconds = (endTime - startTime) / 1000.0;

setText("Time: " + seconds + " sec.");

}

}

public void mouseReleased(MouseEvent evt) { }

public void mouseClicked(MouseEvent evt) { }

public void mouseEntered(MouseEvent evt) { }

public void mouseExited(MouseEvent evt) { }

} // end StopWatchRunner

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