In Java Swing, Change Side Colors Of Frame On Button Click

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.JButton;

import java.awt.BorderLayout;
import java.awt.Color;

import java.util.Random;

public class JColorFrame extends JFrame{

	private JPanel[]sides;
	private JButton btn;
	private Color[]colors;
	private Random random;

	public JColorFrame(){
		super("Colors");
		sides = new JPanel[]{
			new JPanel(),
			new JPanel(),
			new JPanel(),
			new JPanel()
		};
		btn = new JButton("Change");
		colors = new Color[]{
			Color.RED,
			Color.BLUE,
			Color.CYAN,
			Color.PINK
		};
		random = new Random();
	}

	private void createGUI(){
		String[]dirs={
			BorderLayout.NORTH,
			BorderLayout.SOUTH,
			BorderLayout.EAST,
			BorderLayout.WEST
		};
		getContentPane().add(btn);
		for(int i = dirs.length-1; 0<= i; i --)
			getContentPane().add(sides[i], dirs[i]);
	}

	private void bindEvents(){
		btn.addActionListener((e)->{
			SwingUtilities.invokeLater(()->changeColor());
		});
	}

	private void changeColor(){
		int i = random.nextInt(colors.length);
		Color c = colors[i];
		i = random.nextInt(sides.length);
		sides[i].setBackground(c);
	}

	private void launchGUI(){
		createGUI();
		bindEvents();
		pack();
		setLocationRelativeTo(null);
		setVisible(true);
		setDefaultCloseOperation(DISPOSE_ON_CLOSE);
	}

	public static void main(String[]args){
		SwingUtilities.invokeLater(()->{
			new JColorFrame().launchGUI();
		});
	}
}

Download