Understanding Mandelbrot set Programming

I have some code that generates the Mandelbrot set fractal in a GUI. I can't find much information on it, and I'd really like to have the intuition behind how it is generated in java. If someone could please give an intuitive explanation as to what is going on in this code, it would be greatly appreciated:

import java.awt.Graphics;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
 
public class Mandelbrot extends JFrame {
 
    private final int MAX_ITER = 570;
    private final double ZOOM = 150;
    private BufferedImage I;
    private double zx, zy, cX, cY, tmp;
 
    public Mandelbrot() {
        super("Mandelbrot Set");
        setBounds(100, 100, 800, 600);
        setResizable(false);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        I = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_RGB);
        for (int y = 0; y < getHeight(); y++) {
            for (int x = 0; x < getWidth(); x++) {
                zx = zy = 0;
                cX = (x - 400) / ZOOM;
                cY = (y - 300) / ZOOM;
                int iter = MAX_ITER;
                while (zx * zx + zy * zy < 4 && iter > 0) {
                    tmp = zx * zx - zy * zy + cX;
                    zy = 2.0 * zx * zy + cY;
                    zx = tmp;
                    iter--;
                }
                I.setRGB(x, y, iter | (iter << 8));
            }
        }
    }
 
    @Override
    public void paint(Graphics g) {
        g.drawImage(I, 0, 0, this);
    }
 
    public static void main(String[] args) {
        new Mandelbrot().setVisible(true);
    }
}