Beginning Java Script Help, Please!

[gradelover924]

I'm self-studying computer science for enrichment, and I have to say the first thing I gained was a new-found respect for this field and those in it. With that said, I'm so dang confused on my last homework problem that concerns applets. I would appreciate any help I can get. But I'm sure what's hard for me is simple for you hehe.

The question asks to make an applet emulating a banner ad. The ad should display a message alternating "East or West" and "Java is Best" every 2 seconds.

Here is the prototype code I've been given:

// This applet displays a message moving horizontally
// across the screen.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Banner extends JApplet
implements ActionListener
{
private int xPos, yPos; // hold the coordinates of the banner

public void init()
{
Container c = getContentPane();
c.setBackground(Color.WHITE);
xPos = c.getWidth();
yPos = c.getHeight() / 2;
Timer clock = new Timer(30, this); // fires every 30 milliseconds
clock.start();
}

// Called automatically after a repaint request
public void paint(Graphics g)
{
super.paint(g);
g.drawString("Hello, World!", xPos, yPos);
}

// Called automatically when the timer fires
public void actionPerformed(ActionEvent e)
{
Container c = getContentPane();

// Adjust the horizontal position of the banner:
xPos--;
if (xPos < -100)
{
xPos = c.getWidth();
}

// Set the vertical position of the banner:
yPos = c.getHeight() / 2;

repaint();
}
}

Here are the hints the book includes (they didn't help me much )

At the top of your class define a variable that keeps track of which message is to be displayed. For example, private int msgID = 1;

In the method that processes the timer events, toggle msgID between 1 and -1: msgID = -msgID

Don't forget to call repaint.

In the method that draws the text, obtain the coordinates for placing the message:
Container c = getContentPane();
int xPos = c.getWidth() / 2 - 30;
int yPos = c.getHeight() / 2;

Then use a conditional statement to display the appropriate message:
if (msgID == 1)
{
...
}
else // if msgID == -1
{
...
}

THANK YOU AGAIN FOR YOUR HELP!

[Tamlin]

So what, specifically, is your question? Which particular part is confusing you?

[gradelover924]

What throws me off is this msgID thing they're talking about in the hints. I understand the defining a variable, but the msgID = -msgID perplexed me. "Don't forget to call repaint" didn't help me at all. I think that's the source of my confusion.

[U'ziel]

Let me start by saying I dont know Java but most code is more or less the same structure. msgID is used as a switch variable, the simplest example of this is binary code 1 and 0.

for example;
var msgID

if (msgID == 1) {
echo "hello world";

} else if (msgID == 0) {
echo "goodbyle world";

}

for example. If the switch is equal to 1 the code outputs hello world. if its 0 goodbye world. Simple.

repaint is a function you have right at the bottom of your sample code to change the text and position it where you have set it. So you would want something like;

if (msgID == 1) {
repaint(1);

} else if (msgID == -1) {
repaint(-1);

}

Your using the switch in the code to determine the action to take and the func to do the action and re-set the variable so it knows the next action to take, if that makes sense?

after this line "private int xPos, yPos; // hold the coordinates of the banner"
add

private int msgID = 1;

Hope this explains it a little and helps you on your way. Tell your tutor that silverlight would be a much better use of your time for programming a rotating banner add