java.lang.ClassNotFoundException (main class not found)

Posted on 2009-03-30
Last Modified: 2013-12-15

I was working with a 2D graphing example (actually got the example from here) and I was trying to plot some additional points .

After writing code to do so I noticed when running the program the code was stepping through the old code (ie not running sequentially, making bizarre jumps, etc)

So after some googling I decided to clean my project (Project --> Clean)

Now I'm getting an error that says the main class cannot be found, which is quite odd since it was working fine until I "cleaned" it.

I am using java 1.6 and the latest version of eclipse.  Below is my code.

Thanks !!


import javax.swing.*;

import java.awt.*;

import java.util.*;

public class DrawGraphExam extends JFrame


    public DrawGraphExam()


        super("Glove Data Representation");




        Container c = getContentPane();

        c.setLayout(new BorderLayout());

        Graph gloveGraph = new Graph(getPoints());

        //c.add(new Graph(getPoints()));





    private HashMap getPoints()


        HashMap points = new HashMap();

        points.put(new Integer(6), new Integer(5));

        points.put(new Integer(3), new Integer(3));

        points.put(new Integer(7), new Integer(4));

        points.put(new Integer(1), new Integer(7));

        points.put(new Integer(4), new Integer(2));

        return points;


    public static void main(String[] args)



        new DrawGraphExam().show();


    	//DrawGraphExam gloveGraph  = new DrawGraphExam();




    //public void plotPoint()


class Graph extends Canvas


    private HashMap points;

    private int x0;

    private int y0;

    private int b = 25;

    private int gap = 20;

    private int tw = 5;

    //begin berg's code

    private int xOld = 0;

    private int yOld = 0;

    private int xCurrent;

    private int yCurrent;

    //end berg

    public Graph(HashMap points)


        this.points = points;



    public void paint(Graphics g)







    public void drawLine(Graphics g)


        Dimension d = getSize();

        x0 = b;

        y0 = d.height - b;

        Graphics2D g2 = (Graphics2D)g;


        g2.setStroke(new BasicStroke(1.5f));

        g2.drawLine(x0, y0, d.width-x0, y0); // horizontal line

        g2.drawLine(x0, y0, x0, b); // vertical line


        int ticksY = (int) (y0 - b)/gap;

        int ticksX = (int) (d.width-2*x0)/gap;

        int yx = y0;

        for(int i=0; i<ticksY; i++) // draw vertical ticks


            yx -= gap;

            g2.drawLine(x0, yx, x0-tw, yx);

            g2.drawString(String.valueOf(i*10), x0, yx);


        int xx = x0;

        for(int i=0; i<ticksX; i++) // draw horizontal ticks


            xx += gap;

            g2.drawLine(xx, y0, xx, y0+tw);

            g2.drawString(String.valueOf(i*10), xx, y0);



    public void drawPoint(Graphics g){

        Graphics2D g2 = (Graphics2D)g;


        g2.setStroke(new BasicStroke(1f));

        g2.drawLine(xOld, yOld, xCurrent, yCurrent);

        System.out.println("drawing point at " + xOld);



    public void setPoint(int y){

    	xCurrent = xOld + 10; // for now making increments of 5

    	yCurrent = y;


    private void drawPoints(Graphics g)


        if(points != null)


            Graphics2D g2 = (Graphics2D)g;

            g2.setStroke(new BasicStroke(1f));

            ArrayList list = new ArrayList(points.keySet());

            Collections.sort(list); // sorts list of x-set

            Iterator xset = list.iterator();

            int x,y;

            int cX = -1, cY = -1;

            int r = 3;



                Integer key = (Integer);

                x = x0 + (key.intValue() * gap);

                y = y0 - (((Integer)points.get(key)).intValue() * gap);


                if(cX > 0 && cY > 0)


                    g.drawLine(cX, cY, x, y);


                cX = x;

                cY = y;





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Question by:bryanberg
LVL 92

Expert Comment

Comment Utility
check your java file is inside a source folder in your project
and make sure you are running the right class

LVL 15

Expert Comment

Comment Utility
what's your classpath? missed classpath=.\;    ?

Expert Comment

Comment Utility
It's a problem with your project or file names, not your code.  I can compile and run the code you provided just fine.
LVL 86

Accepted Solution

CEHJ earned 500 total points
Comment Utility
Now I'm getting an error that says the main class cannot be found, which is quite odd since it was working fine until I "cleaned" it.

Just try rebuilding the project and running again

Author Closing Comment

Comment Utility
I had to remove the the source folder and than readd it in order to prompt the rebuild.  For some reason my code was not rebuilding on its own, eventhough I had the option selected to build automatically. Anyone had issues like this ?

Thanks !!

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