Thread: Help with Java code

Hello, I'm making a Java code for school but unfortunately I have some issues.

This is my script til now on:

import java.awt.*;
import javax.swing.*;
import javax.swing.event.*;
 
 
public class Cirkels extends JFrame{
	public static void main(String[] args) {
 
		Cirkels w = new Cirkels();
		w.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		w.setSize(800,650);
		w.setVisible(true);
 
			}
 
	private JSlider slider;
	private JLabel tekstslider;
	private Paneel mijnpaneel;
 
 
	public Cirkels(){
 
 
		mijnpaneel = new Paneel();
		mijnpaneel.setBackground(Color.GRAY);
		mijnpaneel.setOpaque(true);
 
 
		slider = new JSlider(SwingConstants.HORIZONTAL, 0, 200, 10);
		slider.setMajorTickSpacing(10);
		slider.setPaintTicks(true);
 
		slider.addChangeListener(
				new ChangeListener(){
					public void stateChanged(ChangeEvent e){
					mijnpaneel.setD(slider.getValue());
 
					}
				}
				);
 
		add(slider, BorderLayout.SOUTH) ;
		add(mijnpaneel, BorderLayout.CENTER) ;
 
			}
 
public class Paneel extends JPanel{
 
	private int d  = 10;
	public void paintComponent (Graphics g) {
		super.paintComponent (g);
		g.setColor(Color.WHITE);
		g.drawOval(25, 100, d, d);
		g.drawOval(175, 100, d, d);
		g.drawOval(325, 100, d, d);
		g.drawOval(475, 100, d, d);
		g.drawOval(625, 100, d, d);
		g.drawOval(100, 200, d, d);
		g.drawOval(250, 200, d, d);
		g.drawOval(400, 200, d, d);
		g.drawOval(550, 200, d, d);
 
 
	}
 
	public void setD(int newD){
	d = (newD >= 0 ? newD : 10); 
	repaint();
	}
 
	public Dimension getPrefferedSize() { 
		return new Dimension(200,200);
	}
 
	public Dimension getMinimumSize() {
		return getPrefferedSize();
	}
 
 
	 }
}

I want to add a JButton to make the ovals different colors, so for example:
JButton for Red and a JButton for Blue, but when I add the buttons the whole layout mess up and no buttons appear...
Can someone help me with adding the buttons?

Sorry for my English, I'm Dutch

Sorry but how can I use the highlight tags?
And I know the general rules for adding a JButton but I can show with a picture what happens.

Before adding a simple JButton:
goed.jpg

After adding JButton:
fout.jpg

The whole layout changes, and the ovals dissapear.

Thank you for the guides, I'm really a beginner in Java and I find it also hard to read English articles but I read them and I understand what they mean but like when I try to fix my code it won't happen. I changed the code btw with the tags

--- Update ---

I think there is not very much code needed to add 2 buttons which sets the color of the Oval

Programming is frustrating haha, I worked for 5 hours on this piece of code.

g.setColor(Color.RED);

This will set the ovals to another color, but the problem is that I can't add a JButton to the script if I know how to do that without messing everything up I think I can solve it myself.

Okay thank you, I'm further now and I managed to make a button.
My code:

		JButton zwart = new JButton("Zwart");
		add(zwart, BorderLayout.PAGE_START);
		KnopHandler kh = new KnopHandler();
		zwart.addActionListener(kh)(
		new ActionListener(){
			public void actionPerformed(ActionEvent e){
						g.setColor(Color.BLACK);
			}
		}
		);

It gives 2 errors at KnopHandler kh = new KnopHandler();
and at zwart.addActionListener(kh)(

It says: KnopHandler can't not be resolved in a type

--- Update ---

Okay thank you, I'm further now and I managed to make a button.
My code:

		JButton zwart = new JButton("Zwart");
		add(zwart, BorderLayout.PAGE_START);
		KnopHandler kh = new KnopHandler();
		zwart.addActionListener(kh)(
		new ActionListener(){
			public void actionPerformed(ActionEvent e){
						g.setColor(Color.BLACK);
			}
		}
		);

It gives 2 errors at KnopHandler kh = new KnopHandler();
and at zwart.addActionListener(kh)(

It says: KnopHandler can't not be resolved in a type