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

ID: 24024654
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

ID: 24025704
what's your classpath? missed classpath=.\;    ?

Expert Comment

ID: 24031888
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
ID: 24032449
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

ID: 31564605
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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