PLeazzzzzzz help with scrolling application

Question

Hello all,
Basically, I want a JFrame that allows the user to scroll down if the monitor size doesn't allow the user to see the entire contents of the JFrame. The problem is that the JPanel is larger than the JScrollPane. However, it doesn't allow me to scroll down and see the rest of the components on the panel?????????????????????????
thanks for your help!
import java.awt.*;
import javax.swing.*;
public class WindowFrames extends JFrame
private JScrollPane scrollPane;
private JPanel mainPanel;
private Container cp, scp;
private static final int WIDTH = 500, HEIGHT = 500;
public WindowFrames()
setTitle( "Scrolling Pane Application" );
setSize(WIDTH, HEIGHT );
setBackground( Color.gray );
setVisible(true);
// setResizable(false);
cp = getContentPane();
cp.setLayout(null);
mainPanel = new JPanel();
mainPanel.setBounds(0,0,2*WIDTH,2*HEIGHT);
mainPanel.setBackground(Color.red);
mainPanel.setLayout(null);
JTextArea a,b,c;
a = new JTextArea();
a.setVisible(true);
a.setBounds(0,0,200,200);
b = new JTextArea();
b.setVisible(true);
b.setBounds(0,400,200,200);
c = new JTextArea();
c.setVisible(true);
c.setBounds(0,700,200,200);
mainPanel.add(a);
mainPanel.add(b);
mainPanel.add(c);
scrollPane = new JScrollPane(mainPanel,JScrollPane.VERTICAL_SCROLLBAR_ALWAYS ,JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED );
scrollPane.setBounds(0,0,WIDTH, HEIGHT);
cp.add(scrollPane);
repaint();

Answer 1

Since you are using a null layout manager, you have to manually set the
preferrred size of the mainPanel. JScrollPane use the perfered size of it children to determine how to display the scrool bar.
add this to your code and the scrool bar will show up.
mainPanel.setPreferredSize(new Dimension(200, 900));
in your code:
==================
mainPanel.add(a);
mainPanel.add(b);
mainPanel.add(c);
mainPanel.setPreferredSize(new Dimension(200, 900));