Ciao a tutti,
ho fatto questa semplice interfaccia grafica. La compilo e mi segnala 3 errori, ma poi produce un file class funzionante....che dite?

codice:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ButtonTest3{
	public static void main(String[] args){
		ButtonFrame frame = new ButtonFrame();
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setVisible(true);
	}
}

class ButtonFrame extends JFrame{
	public ButtonFrame(){
		setTitle("ButtonTest");
		setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);

		//aggiunge il pannello al frame

		ButtonPanel panel = new ButtonPanel();
		add(panel);
	}

	public static final int DEFAULT_WIDTH = 300;
	public static final int DEFAULT_HEIGHT = 200;
}

class ButtonPanel extends JPanel implements ActionListener{
	public ButtonPanel(){

// crea i pulsanti

		JButton yellowButton = new JButton("Yellow");
		JButton blueButton = new JButton("Blue");
		JButton redButton = new JButton("Red");

		// aggiunge i pulsanti al pannello

		add(yellowButton);
		add(blueButton);
		add(redButton);

		// associa le azioni ai pulsanti

		yellowButton.addActionListener(this);
		blueButton.addActionListener(this);
		redButton.addActionListener(this);
	}

    public void actionPerformed(ActionEvent event){
    	Object source = event.getSource();
    	if(source == yellowButton) setBackground(Color.YELLOW);
    	 else if(source == blueButton) setBackground(Color.BLUE);
    	 else if(source == redButton) setBackground(Color.RED);
    }


	}