Mandelbrot set on Java - Is there something wrong with my algorithm?

Question

I was asked to display the Mandelbrot set on Java but I have encountered a problem. My teacher and I both are stumped to why this doesn't run correctly.

I reckon it has something to do with the algorithm or the complex class since all values except positive/negative 1 and 0 escape to infinity after two iterations.

import javax.swing.*;
import java.awt.*;

public class fractal {

        public class complex { double re; double im;
                public complex(double x, double y){
                    this.re =x;
                    this.im =y;
                }
                public double mag(){
                    return (Math.sqrt(re*re+im*im));
                }
        }


static int xcord = 500;
static int ycord = 500;

 public static void main(String[] args) {   
        JFrame myFrame = new JFrame("Question 10");
        myFrame.setSize(xcord,ycord);
        JPanel myPane = (JPanel) myFrame.getContentPane();
        myPane.add(new paint());
        myFrame.setVisible(true);
    }
}

class paint extends JComponent {

        public complex add(complex a, complex b){
            return new complex(a.re+b.re,a.im+b.im);
            }
         public complex multiply(complex a,complex b) {
              return new complex((a.re*b.re)-(a.im*b.im),(a.re*b.im)+(a.im*b.re));
            }




public void paint (Graphics g){

    final int SCALE =100; //pixels per unit
    int itr = 0;
    int max_itr = 30;
    Color clr = Color.black;
    g.translate(fractal.xcord/2, fractal.ycord/2); // Move origin to center of frame


    for (int x = -2*SCALE; x <= 1*SCALE; x++){

        for (int y = -1*SCALE; y <= 1*SCALE; y++){

            complex C = new complex(x/SCALE,y/SCALE); // math done on unscaled values
            complex z = C;
            itr = 0;

            while ( z.mag() <= 4.0 && itr < max_itr){ 

                z = add(multiply(z,z),C);   
                itr++;

                }

            if (itr == max_itr){
                clr = Color.black;
            }

            else{
                clr = new Color((int) Math.round(itr*8.5),(int) Math.round(itr*8.5),(int) Math.round(itr*8.5)); // Colouring of fractal
            }

            g.drawOval(x, y, 2, 2);
            g.setColor(clr);

            }
        }
    } 
}

Answer 1

I think that you have to wide boundaries. [-200,100], where you should have [-2,1] for Re and [-1,1] for Im.

complex C = new complex(x/SCALE,y/SCALE);

Answer 2

              complex C = new complex(x/SCALE,y/SCALE); // math done on unscaled values

Since x and y are ints (and SCALE too), you're doing integer division here.

Try this instead:

              complex C = new complex((double)x/SCALE,(double)y/SCALE); // math done on unscaled values

By the way, this is not an error, but add() and multiply() should really be methods of the Complex class, which should be capitalised according to the Java naming convention.