Jpanel skal deles i fire

Kode 

import java.awt.Color;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.BoxLayout;

public class Test extends JFrame {
    private JPanel parts[];
    private final static Color COLORS[] = {
        Color.red, Color.green, Color.blue, Color.magenta, Color.yellow, Color.black
    };
    public Test() {
        super("Delt i fire");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        getContentPane().setLayout(new BoxLayout(getContentPane(), BoxLayout.Y_AXIS));
        parts = new JPanel[4];

        for (int i = 0; i < parts.length; i++) {
            parts[i] = new ColoredPanel(i);
            getContentPane().add(parts[i]);
        }
        setSize(600, 400);
        setVisible(true);
    }

    private class ColoredPanel extends JPanel {
        private int index;

        public ColoredPanel(int colorIndex) {
            this.index = colorIndex;
            setBackground(COLORS[index % COLORS.length]);
            addMouseListener(new MouseAdapter() {
                public void mouseClicked(MouseEvent e) {
                    setBackground(COLORS[(++index) % COLORS.length]);
                }
            });
        }
    }

    public static void main(String args[]) {
        new Test();
    }
}