[Java] Har kört fast lite med Swing

package main;

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

public class main {
	
	public static void main(String[] args){

		// Frames
		
		JFrame mainFrame = new JFrame("It's the frame");
		
		// Panels
		
		JPanel panel = new JPanel();
		
		// Buttons
		
		JButton button1 = new JButton();
		JButton button2 = new JButton();
		JButton button3 = new JButton();
		JButton button4 = new JButton();
		
		// Frame
		mainFrame.setVisible(true);
		mainFrame.add(panel);
		mainFrame.setResizable(false);
		mainFrame.setSize(500, 150);
		
		// Panel
		
		panel.add(button1);
		panel.add(button2);
		panel.add(button3);
		panel.add(button4);
		
		// Button 1
		
		button1.setBackground(Color.RED);
		button1.setForeground(Color.RED);
		button1.setPreferredSize(new Dimension(100, 100));
		button1.setBorder(null);
		
		// Button 2
		
		button2.setBackground(Color.GREEN);
		button2.setForeground(Color.GREEN);
		button2.setPreferredSize(new Dimension(100, 100));
		button2.setBorder(null);
		
		// Button 3
		
		button3.setBackground(Color.BLUE);
		button3.setForeground(Color.BLUE);
		button3.setPreferredSize(new Dimension(100, 100));
		button3.setBorder(null);
		
		// Button 4
		
		button4.setBackground(Color.YELLOW);
		button4.setForeground(Color.YELLOW);
		button4.setPreferredSize(new Dimension(100, 100));
		button4.setBorder(null);
		
		}
	}