[Java] Non vengono visualizzati tutti i pulsanti inseriti

[Azzurra85]

Ciao a tutti!!!!
Ho un problema nel seguente codice: non riesco a visualizzare tutti i bottoni che inserisco nel JPanel center tramite le barre di scorrimento, perchèèè???? che sbaglio???

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.FlowLayout;
import javax.swing.BoxLayout;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JToggleButton;
import javax.swing.border.EtchedBorder;

public class Frame extends JFrame {
	public JDialog dialog;
	
	Frame(){
		
		this.setBounds (30, 30, 1100, 750);
		this.getContentPane().setLayout(new FlowLayout());
		
		dialog = new JDialog(this,"Ciao",false);
		JPanel internal = new JPanel(new BorderLayout());
		
		JPanel center = new JPanel();
		center.setLayout(new BoxLayout(center, BoxLayout.Y_AXIS));
		center.setPreferredSize(new Dimension(300,50));
		center.setBorder(new EtchedBorder(EtchedBorder.RAISED));
		
		JScrollPane scroll = new JScrollPane(center,JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
		scroll.setPreferredSize(new Dimension(200,50));
		
		internal.add(scroll,BorderLayout.CENTER);
		
		center.add(new JToggleButton("ciao"));
		center.add(new JToggleButton("ciao"));
		center.add(new JToggleButton("ciao"));
		center.add(new JToggleButton("ciao"));
		center.add(new JToggleButton("ciao"));
		center.add(new JToggleButton("ciao"));
		center.validate();
		
		JPanel south = new JPanel(new FlowLayout());
		south.add(new JToggleButton("ehi"));
		south.add(new JToggleButton("ok"));
		
		internal.add(south,BorderLayout.SOUTH);
		
		dialog.add(internal);
		dialog.pack();
		dialog.setVisible(true);
		this.setVisible(true);
		
	}
	public static void main(String args[]){
		Frame f = new Frame();
	}
}