Circle Painter

package so;

import java.awt.*;
import java.util.Random;
import java.util.function.*;
import javax.swing.*;

public class CirclePainter {

    public static void main(String[] args) {
        JFrame frame = new JFrame("Circle Painter");
        frame.setLayout(new FlowLayout());

        //java 8 style
        Function<Integer, int[]> fiftyShadesOfGray = (i -> new int[]{4*i,4*i,4*i});

        //pre-java 8 style
        DiameterToColor anotherFunc = new DiameterToColor() {
            @Override
            public int[] getColor(int i) {
                return new int[]{20+4*i,255-4*i,100+2*i};
            }
        };

        JPanel gray = new MyPanel(fiftyShadesOfGray);
        JPanel colorful = new MyPanel(anotherFunc);

        frame.add(gray);
        frame.add(colorful);

        frame.pack();
        frame.setLocationRelativeTo(null);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    private static class MyPanel extends JPanel {
        //better than magic constants hard-coded deep inside method
        private static final int X = 0, Y = 1, DIAM = 2,
                COLOR_R = 3, COLOR_G = 4, COLOR_B = 5;


        private int width = 500, height = 500;
        private Dimension prefSize = new Dimension(width, height);

        /**
         * array of information about circles, in format
         * x|y|diameter|colorR|colorG|colorG
         */
        private int[][] circles;

        private int maxDiameter = 50;
        private int count = 100;

        //use this if you have java 8
        public MyPanel(Function<? super Integer, ? extends int[]> diamToColor) {
            //optional: seed your random generator for repeatable testing
            long seed = 6194466113533747327L;
            Random ran = new Random(seed);

            circles = new int[count][];
            for (int i = 0; i < count; i++) {
                int x = ran.nextInt(width);
                int y = ran.nextInt(height);
                int d = ran.nextInt(maxDiameter);
                int[] col = diamToColor.apply(d);
                circles[i] = new int[]{x, y, d, col[0], col[1], col[2]};
            }
        }

        //move body of previous constructor here
        //if you don't have java 8
        public MyPanel(DiameterToColor diamToColor) {
            this((Function<Integer, int[]>) diamToColor::getColor);
        }

        @Override
        public Dimension getPreferredSize() {
            return prefSize;
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            for(int[] circle: circles) {
                g.setColor(new Color(circle[COLOR_R], circle[COLOR_G], circle[COLOR_B]));
                g.fillOval(circle[X], circle[Y], circle[DIAM], circle[DIAM]);
            }
        }

    }

    //use java 8 Function instead if avaliable
    private static interface DiameterToColor {

        public int[] getColor(int diameter);
    }

}