Javanull pointer exception while trying to plot a point, help pls :(

Question

Hi, i'm trying to plot mandelbrot's set, but i'm having problem with java logic, or something, i'm using netbeans, i have all the functions needed to calculate if a point belongs to mandelbrot or not, but when it comes to displaying a point, i get a null pointer exception, at the line that is supposed to plot it, here is my code:
* juliabrot.java
* Created on 14 de julio de 2010, 11:42 PM
package Fractales;
import java.awt.Color;
import java.awt.Graphics;
* @author  Omar
public class juliabrot extends javax.swing.JPanel {
    private float tamX=370;
    private float tamY=270;
    public Graphics g;
    /** Creates new form juliabrot */
    public juliabrot() {
        initComponents(); 
        Complejos C=new Complejos(0.0,0.0);
        calcular(-2.0f,-1.25f,0.5f,1.25f,C);
        //repaint();
    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                         
    private void initComponents() {
        canvas1 = new java.awt.Canvas();
        canvas1.setBackground(new java.awt.Color(255, 255, 255));
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
        this.setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(canvas1, javax.swing.GroupLayout.DEFAULT_SIZE, 380, Short.MAX_VALUE)
                .addContainerGap())
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(canvas1, javax.swing.GroupLayout.DEFAULT_SIZE, 280, Short.MAX_VALUE)
                .addContainerGap())
    }// </editor-fold>                       
    // Variables declaration - do not modify                    
    private java.awt.Canvas canvas1;
    // End of variables declaration                  
   public int julia(Complejos z,Complejos x,int max){
    Complejos w=new Complejos();
    int k=0;
    w=z;
    double h=w.modulo(w);
    while(h<=2 && k<=max){
        w=w.cuadradoC(w);
        w=w.sumacomplejos(w, x);
        h=w.modulo(w); 
        k++;
    return k;
public int Mandelbrot(Complejos z,int max){
    Complejos w=new Complejos();
    double h;
    int k=0;
    w=z; 
    h=w.modulo(w);
    while(h<= 4.0 && k<max){
        w=w.cuadradoC(w);
        w=w.sumacomplejos(w, z);
        h=w.modulo(w);
        k++;
    return k;
    public void calcular(float xmin, float ymin, float xmax, float ymax, Complejos c) {
        //g=canvas1.getGraphics();
        int i=0;int j=0;
        int color;
        Complejos z = new Complejos();
        float px, py, dx, dy;
        px = xmin;
        py = ymin;
        dx = (xmax - xmin) / tamX;
        dy = (ymax - ymin) / tamY;
        while(i<=tamX){
            while(j<=tamY){
                z.x=px;
                z.y=py;
                //color=julia(z,c,250);
                color=Mandelbrot(z,250);
                dibujar(g,i,j,color);
                j++;
                py = py + dy;
                z.y=z.y+dy;
            px = px + dx;
            //z.x=z.x+dx;
            py = ymin;
            j=0;
            i++;
    public void dibujar(Graphics g, int i, int j, int color) {
        int maxiter = 250;
        //System.out.println(i + "D" + j);
        if (color >= maxiter) {
            g.setColor(Color.BLACK);
            g.fillOval(i, j, 1, 1);
        } else if (color > maxiter / 8) {
            g.setColor(Color.ORANGE);
            g.fillOval(i, j, 1, 1);
        } else if (color > maxiter / 10) {
            g.setColor(Color.RED);
            g.fillOval(i, j, 1, 1);
        } else if (color > maxiter / 20) {
            g.setColor(Color.BLUE);
            g.fillOval(i, j, 1, 1);
        } else if (color > maxiter / 40) {
            g.setColor(Color.YELLOW);
            g.fillOval(i, j, 1, 1);
        } else if (color > maxiter / 100) {
            g.setColor(Color.GREEN);
            g.fillOval(i, j, 1, 1);
        } else {
            //System.out.println(i+"D"+j);
            g.setColor(Color.CYAN);  //i get the null pointer here, or in any other that belongs to mandelbrot set
            g.fillOval(i, j, 1, 1);
    /*@Override
    public void paint (Graphics G){
        Complejos C=new Complejos(0.0,0.0);
        calcular(-2.0f,-1.25f,0.5f,1.25f,C);
}I'm using netbeans, to execute it i just add it to a jframe, i don't know what i'm doing wrong, some help would be appreciated.
Thanks in advance

Answer 1

DarrylBurke wrote:
Recommended reading: [The Java Tutorials|http://download.oracle.com/docs/cd/E17409_01/javase/tutorial/]
Code comments:
-- Inconsistent use of horizontal and vertical whitespace, makes the code very difficult to read
-- Variable declarations interspersed with executable code
-- Mixing heavy and lightweight components (JPanel and Canvas)
-- Incorrect approach to custom painting
-- Invoking a method with an uninitialized class field as a parameter
Seriously, learn some basics before trying to copy code from here and there, throwing it at the wall and hoping it'll stick.
dbWell, the whitespace are handled by netbeans, didn't copied the code, but most codes that you'll find to make julia and mandelbrot sets will be very similar, there are craploads of fully working java codes for this , if had copied it would work, as for the rest, yes, i'm not a java expert, that's why i'm asking for help here, if i had enough time to become an expert, i wouldn't be asking for help here.
As for the stack trace, i'm getting this:
java.lang.NullPointerException
at Fractales.juliabrot.dibujar(juliabrot.java:145)
at Fractales.juliabrot.calcular(juliabrot.java:109)
at Fractales.juliabrot.<init>(juliabrot.java:25)
at Fractales.Visualizacion.init(Visualizacion.java:25)
at sun.applet.AppletPanel.run(AppletPanel.java:425)
at java.lang.Thread.run(Thread.java:619)
As i've said, Vizalizacion just creates a new panel, and adds it.
Edited by: omar.nus on Jul 15, 2010 12:20 PM