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Need help With a Java Prodject

 
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Selphania

I watch Dragonball-Z



Joined: 06 Mar 2007
Posts: 15
Location: Behind you.

PostPosted: Thu May 03, 2007 1:53 pm    Post subject: Need help With a Java Prodject Reply with quote

When i run this, i get an error i have never seen before , java.lang.NoSuchMethodError: main
Exception in thread "main"

i use eclipse SDK, and a up to date java, if anyone could please find out what is wrong i will be very thankful.

the program is below.

thanks for reading this post, please reply.

package Demos;

public class Rectangle {
private int x, y;
private int width, height;

public Rectangle() {
this(0, 0, 0, 0);
}
public Rectangle(int width, int height) {
this(0, 0, width, height);
}
public Rectangle(int x, int y, int width, int height) {
this.x = x;
this.y = y;
this.width = width;
this.height = height;
}

}
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ickyb0d

Evangelion is cool



Joined: 08 May 2006
Posts: 407
Location: Sniper Island... LOCK ON!

PostPosted: Thu May 03, 2007 2:44 pm    Post subject: Reply with quote

if that's your entire program, aren't you missing a main function? Something like what's below inside of your Rectangle class?

Code:
public static void main(String[] args)  {
  //insert awesomeness here   
}

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Selphania

I watch Dragonball-Z



Joined: 06 Mar 2007
Posts: 15
Location: Behind you.

PostPosted: Fri May 04, 2007 9:27 am    Post subject: Reply with quote

I am very new so sorry my noob knowlage of java. Where does the main funcion need to be? And what do you mean by "main function". DO you mean i need to have it spit out a calculation?

please help

thanks for answering
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ickyb0d

Evangelion is cool



Joined: 08 May 2006
Posts: 407
Location: Sniper Island... LOCK ON!

PostPosted: Fri May 04, 2007 11:12 am    Post subject: Reply with quote

Yeah, i haven't done java in a LONG time, but what you have above is basically a class definition. If you want to execute a program, i believe Java looks for some "main" function within one your class(es) to execute. Since you have no main function, it doesn't know what to execute and that's probbaly why it's throwing an exception. So if this is the only code you're using in your project, then you're most likely just missing this main function.

Heh, i also may be completely wrong, i haven't done java in a long time. If i get some time, maybe i'll mess around and see what i can come up with and see why it isn't working.

You can put the main function anywhere inside your class. Something like...

Code:


package Demos;

public class Rectangle {
  private int x, y;
  private int width, height;

  public Rectangle() {
    this(0, 0, 0, 0);
  }
  public Rectangle(int width, int height) {
    this(0, 0, width, height);
  }
  public Rectangle(int x, int y, int width, int height) {
    this.x = x;
    this.y = y;
    this.width = width;
    this.height = height;
  }

  public static void main(String[] args)  {
    //insert awesomeness here   
  }
}

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MrVince

Kohai (後輩)

Kohai (後輩)


Joined: 13 Dec 2005
Posts: 909

PostPosted: Fri May 04, 2007 1:22 pm    Post subject: Reply with quote

Icky is right, so I won't repeat all of what he said.

You are creating a Rectangle class. The question I have for you is, what do you want to do with it? Do you need to make a test to test the functionality of the Rectangle class? If you just want it to compile, you don't need to have a main method. You would just go to the directory the java file is and type:
Code:
javac Rectangle.java


The problem is that you will not be able to test this class unless you either:

1. Create a test class that references the Rectangle class and has a main() method.
-or-
2. Create a main method in class Rectangle to test the functionality.

For all you non-techs reading this, what I'm basically asking him is no different than someone handing me a fork and saying "make it work" when there is no food nor plate around.

I can tell by the level of style of the code you have typed so far it's not yours. I'm guessing it's some starting code provided by your instructor. I don't mind helping you out on this assignment but you're going to have to figure some of this stuff out on your own.
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Selphania

I watch Dragonball-Z



Joined: 06 Mar 2007
Posts: 15
Location: Behind you.

PostPosted: Thu May 10, 2007 7:17 pm    Post subject: Reply with quote

Well to answer your question,
I was just experimenting with new classes and found a demo.

my java teacher is fairly new to java so i have trying to learn more on my own, i didnt even know i needed a main. Thanks for your help, both of you.
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DEATHGOD

Moderator

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Joined: 21 Nov 2005
Posts: 1098
Location: Ohio

PostPosted: Fri May 11, 2007 12:01 am    Post subject: Reply with quote

Ill post some examples tomorrow working with the GUI.
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Tenchi

I watch Dragonball-Z



Joined: 16 Mar 2007
Posts: 12
Location: Kansas

PostPosted: Fri May 11, 2007 8:54 pm    Post subject: Reply with quote

Iv been in a java class for the last semester of my Sr. year in HS. the Main class is the Driver program basicly. you dont NEED it if you are simply making a class like rectange.

the way you would use a Main method, is basicly like this.
this is where this file ends, suppose that you have these classes already compiled. Rectangle *drawRectangle is a method of class Rectangle*, and Circle *where drawCircle is a method of class Circle*.


public class *file name*
{
public static void main()
{
Rectangle.drawRectangle(20,20,20,20);
Circle.drawCircle(20,20,20,20);
}
}
___________________________________
the main method here is just used as a way to controll the classes that are already made but you dont need it to simply create a class.


PS
i compiled your java program * w/o the package Demos;* the reason you were getting that error is because Java does not know wtf package Demos IS* using JCreator *a handy editor, ill provide a link for the free download* and it compiles fine and w/o error. however it wont DO anything unless you access it from another program with paramaters being sent down like above, but probably you wana create an object of the Rectangle class...... "Rectangle q = new Rectangle(x,y,length,width);" something like that
also you need some code to actually Draw the rectangle... here is a snidbit to let you draw it.

when you make the method, you NEED "Graphics g" in there or it wont do a thing =D

public void paint(Graphics g)
{
g.drawRect(x,y,width, height);
}
=D anyway, if you have some questions or need some help debugging just gime a shout. btw here is the link for JCreator, this handy little program just simplifies things for you and allows you to view applets and run programs w/o command prompt.

http://www.jcreator.com/download.htm
You want the JCreator LE version, that is the free version. tho you can BUY the pro version if ya really want to Confused
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