JScrollPane z JPanel nic nie widzisz - java, swing, jframe, jpanel, jscrollpane

Dodaję do JFrame JSrollPane. ScrollPane zawiera JPanels. Ale mam problem, kiedy dodaję pierwszy JPanel do ScrollPane i nic nie widzę, kiedy dodaję JPanela do JFrame Widzę JPanels. Więc gdzie popełniam błąd? Tutaj kod:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollBar;
import javax.swing.JScrollPane;
import javax.swing.JTextField;

public class AddingJPanels {

public static void main(String... args) {
JFrame jF = new JFrame();
PanelMain pM = new PanelMain();

Panel p = new Panel("sas");
JPanel jp = makeJPanel(10);
p.setPreferredSize(new Dimension(600,600));
JScrollPane scroll = new JScrollPane();
scroll.add(jp);
JScrollBar verticalPane = scroll.getVerticalScrollBar();
verticalPane.setValue(verticalPane.getMinimum());
verticalPane.setValue(20);
//scroll.setPreferredSize(new Dimension(570, 300));
scroll.setPreferredSize(new Dimension(400,500));
pM.add(scroll);
//JTabbedPane tB = new JTabbedPane();
//tB.addTab(":]", null, pM, "Tab 3");
jF.add(jp);
jF.setSize(new Dimension(500,500));
jF.setVisible(true);
}






static JPanel makeJPanel(int i){
JPanel jPl = new JPanel();
jPl.setLayout(new GridLayout(i,0));
JLabel lebel;

for(int j=0;j<i;++j){
JPanel p = new JPanel();
p.setLayout(new GridLayout(2,2));
JButton b = new JButton("asa");
p.add(b);
p.setBorder(BorderFactory.createLineBorder(Color.black));
p.setPreferredSize(new Dimension(400,400));
lebel = new JLabel("Napis: "+j);
p.add(lebel);
JTextField jTF = new JTextField("Nic",20);
p.add(jTF);
jPl.add(p);
}
return jPl;
}
}

class Frame extends JFrame {
public Frame() {
super("Frame");
this.setPreferredSize(new Dimension(200, 200));

}

public void see() {
this.setVisible(true);
}
}

class PanelMain extends JPanel {
JButton b = new JButton("press me");

public PanelMain() {
this.add(b);
b.addActionListener(new ActionListener(){

@Override
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
System.out.println("Pressed");
}

});
}
}

class Panel extends JPanel {
JLabel l;

public Panel(String s) {
l = new JLabel(s);
this.add(l);
}
}

Kiedy robię jF.add (scroll) nie ma efektu.

Odpowiedzi:

JScrollPane scroll = new JScrollPane(jp);

add () nie działa na JScrollPane. Musisz użyć setViewport () lub przekazać komponent do contstructor.

JScrollPane scroll = new JScrollPane(jp);

lub

JScrollPane scroll = new JScrollPane();
scroll.setViewport(jp);

posługiwać się:

scroll.setViewportView(jp);