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Lauren · Guest

Hello,

Its my first into OO with Java, and this problem had made me
nearly pull my hair out 4da whole day. I have read up the book
I am studying and the internet, cun anyone help me convert the
original main() to suit the Applets init(), start() etc.

I mean, would my constructor become the new init()? I have done it so, and it seemed to come up with a window with just the buttons(start,stop etc).

I have the other things i.e the html sorted.

import java.applet.*;
import java.awt.*;
import java.util.Vector;
import java.awt.event.*;
import javax.swing.*;
import java.awt.Graphics;

public class MultiBallApplet extends JApplet {

public static void main (String [ ] args) {

MultiBallApplet world = new MultiBallApplet(Color.red);

world.show ();
while (true) world.run();
}

private static final int FrameWidth = 600;
private static final int FrameHeight = 400;
private static Color ballColor = Color.red;
private int counter = 0;
private static final int BallArraySize = 10;
private Ball [] ballArray = new Ball [BallArraySize];

public void MultiBallApplet(){
// general application initialization
//setSize (FrameWidth, FrameHeight);
//setTitle ("MultiBall World");
// application specific initialization
for (int i = 0; i < BallArraySize; i++) {
ballArray[i] = new Ball(new Point(10, 15), 5);
ballArray[i].setColor (ballColor);
ballArray[i].setMotion (3.0+i, 6.0-i);
}
}

public void run(){
// then move it slightly
for (int i = 0; i < BallArraySize; i++) {
ballArray[i].move();
Point pos = ballArray[i].location();
if ((pos.x < ballArray[i].radius()) || (pos.x > FrameWidth
-ballArray[i].radius()))
ballArray[i].reflectHorz();
if ((pos.y < ballArray[i].radius()) || (pos.y > FrameHeight - ballArray[i].radius()))
ballArray[i].reflectVert();
}
repaint();
try{
Thread.sleep(10);
} catch(Exception e) {System.exit(0);}
}

public void paint (Graphics g) {
super.paint(g);
for (int i = 0; i < BallArraySize; i++) {
ballArray[i].paint(g);
}
}

}

Arthur Ore · Guest

Hi Lauren,

You are trying to instaniate (create) a new applet passing in the colour
red.You need to create a construcor that accepts a colour

public MultiBallApplet(Color myColour)
{
// your code here
}

Next, are you aware that you code is utilising the default Java constructor
which has no code other than a call to super() in it? Constructors don't
have a return type, in your case "void". See mine above; public void
MultiBallApplet() is a valid method, but it is not a constructor.

Next main(String [] args) is the entry point into an application, whereas
init() is for applets. Hence its main rather than the constructor which
could be replaced.

However, you can keep the main(String [] args) method. Simply add the
following method to your applet.

public void init()
{
main(null);
}

This will call your existing main method

Hope this helps

Arth

"Lauren" <lauril (AT) 37 (DOT) com> wrote

Lauren · Guest

Thanks for thereply Arth, I was making changes to the file at
the time. But the init() method you explained was interesting.

Its just that I have been receiving this error every time
I compile:
"The applet MultiBallApplet does not have a public constructor MultiBallApplet()"

But I do not have MultiBallApplet() now?

Here is the code after I made th changes:
import java.applet.*;
import java.awt.*;
import java.util.Vector;
import java.awt.event.*;
import javax.swing.*;
import java.awt.Graphics;

public class MultiBallApplet extends JApplet {
public static void main (String [ ] args) {

MultiBallApplet world = new MultiBallApplet(Color.red);
world.show ();
while (true) world.run();
}

private static final int FrameWidth = 600;
private static final int FrameHeight = 400;
private int counter = 0;
private static final int BallArraySize = 10;
private Ball [] ballArray = new Ball [BallArraySize];

public MultiBallApplet(Color ballColor){
// application specific initialization
for (int i = 0; i < BallArraySize; i++) {
ballArray[i] = new Ball(new Point(10, 15), 5);
ballArray[i].setColor (ballColor);
ballArray[i].setMotion (3.0+i, 6.0-i);
}
show();
}

public void run(){
// then move it slightly
for (int i = 0; i < BallArraySize; i++) {
ballArray[i].move();
Point pos = ballArray[i].location();
if ((pos.x < ballArray[i].radius()) || (pos.x > FrameWidth - ballArray[i].radius()))
ballArray[i].reflectHorz();
if ((pos.y < ballArray[i].radius()) || (pos.y > FrameHeight - ballArray[i].radius()))
ballArray[i].reflectVert();
}
repaint();
try{
Thread.sleep(10);
} catch(Exception e) {System.exit(0);}
}

public void init(){
main(null);
}

public void paint (Graphics g) {
super.paint(g);
for (int i = 0; i < BallArraySize; i++) {
ballArray[i].paint(g);
}
}

}

Arthur Ore · Guest

Hi Lauren,

I'm not sure what you are saying. I think you are saying it does compile
now, but you don't understand why?

You are correct, you don't have a constructor MultiBallApplet() , but from
the code you have posted you shouldn't need one.

I suspect the message said it couldn't find MultiBallApplet(java.awt.Color)
, which was true at the time.

Every Java class must have at least one constructor. If you don't specify
one, the compiler provides one for you which is effectively :-
MultiBallApplet()
{
super();
}

Once you specify a constructor (as you have now) the compiler will not add
one for you. Before you had a method with the same name as the constructor,
but with a return type of "void" making it a standard method instead of a
constructor. Hence before, you did have a constructor MultiBallApplet()
(provided by the compiler) but effectively it had no code in it. However,
your statement new MultiBallApplet(Color.red) means your code expects to
find a constructor that takes a Color as a parameter. You now have this.

If I've misunderstood and you still have an error please post the contents
and someone may be able to help.

Arth

"Lauren" <Lauriel (AT) 37 (DOT) com> wrote

Kevin Dean [TeamB] · Guest

Lauren wrote:

Lauren · Guest

Thanks Kev, its all dancing now.

"Kevin Dean [TeamB]" <NkOdSePaAnM (AT) datadevelopment (DOT) com> wrote: