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Old 06-30-2004, 01:53 PM   #1
lmellen
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newbie java question


I'm taking a java course this fall at the local community college.
I thought I'd get a jump on the course so I bought " The Java Tutorial - Third Edition,recommended by Amazon.com.
The book is for j2sdk1.3.1. I downloaded j2sdk1.4.2. Will the newer compiler cause program errors when I do the exercises? I copied the code exactly, javac is ok, creates the class file, but when I try java I get:"Execption in thread "main" java.lang.NoSuchMethodError: main
Thanks -- Larry
 
Old 06-30-2004, 02:00 PM   #2
meblost
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Is there a main method in the file you are compiling? What command are you executing to compile?
 
Old 06-30-2004, 03:19 PM   #3
dave_starsky
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What you need to do is make sure that you have a

Code:
public static void main(String [] args)
method somewhere in the class which you are executing. This is where your program will start when you do "java mainClass" or whatever your class is called.
 
Old 06-30-2004, 04:21 PM   #4
lmellen
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This is the code:

import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;

public class ClickMe extends Applet implements MouseListener {
private Spot spot = null;
private static final int RADIUS = 7;

public void init() {
addMouseListener(this);
}

public void paint(Graphics g) {
//draw a black border and a white background
g.setColor(Color.white);
g.fillRect(0, 0, getSize().width - 1, getSize().height - 1);
g.setColor(Color.black);
g.drawRect(0, 0, getSize().width - 1, getSize().height - 1);

//draw the spot
g.setColor(Color.red);
if (spot != null) {
g.fillOval(spot.x - RADIUS, spot.y - RADIUS, RADIUS * 2, RADIUS * 2);
}
}
public void mousePressed(MouseEvent event) {
if (spot == null) {
spot = new Spot(RADIUS);
}
spot.x = event.getX();
spot.y = event.getY();
repaint();
}
public void mouseClicked(MouseEvent event) {}
public void mouseReleased(MouseEvent event) {}
public void mouseEntered(MouseEvent event) {}
public void mouseExited(MouseEvent event) {}
}

It's the same on the tutorial cd that came with the book, it's the same at their website(it's a sun microsystems book.
I don't think they want me to start rewriting code already, but
as dave_starsky stated; also clearly stated in the book:

public static void main(String [] args)

must be used to start all applications.
I can place this above the 4th line of code, if it works.

thanks for the reply -- Larry
 
Old 06-30-2004, 05:06 PM   #5
jlliagre
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main method is needed for applications entry classes, while your class is an applet, so doesn't need a main.
 
Old 06-30-2004, 05:13 PM   #6
coolman0stress
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You've written an applet, you don't need a main to start it. You need to embed it in an html page to view it (either through the browser or the appletviewer).

Compile your code (javac), but obviously don't try to run it.
Then create an html file like this (change the applet attributes though)
Code:
<html>
<body>
  <applet code="MyJava.class" width="300" height="200">
  </applet>
</body>
</html>
Then run it either through the browser (open the html file) or the appletviewer:
Code:
appletviewer MyJavaHtml.html
Also, you should use JApplet instead of Applet now.
 
Old 06-30-2004, 05:34 PM   #7
lmellen
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Thanks coolman0stress, that worked. It was also in the book. I'm trying to do 15 things at once. I should have reviewed better. My fault. Thanks for the reply.
Larry
 
  


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