Question

I am having two problems with the layout of my gui.
I am using a JTabbedPane to hold two JPanels, each panel has a selection of buttons and text areas, and each is laid out using GridBagLayout.
In one of my Panels I have a JScrollPane which uses a JTextArea. When I append anything to this text area and then click off the gui so it no longer has focus, or if I change the tab, the sizes of all the text fields and the text are changed to be as small as they can be.

To further illustrate my problem, here are before and after pictures of when i click off the gui after appending to the text area:

Here is the code that I use to add the JTextArea to the Panel:

table = new JTextArea();
    table.setEditable(false);
    JScrollPane sp = new JScrollPane(table);
    sp.setSize(40, 10);
    c.insets = new Insets(10,10,10,10);
    c.gridx = 1;
    c.gridwidth = 4;
    c.gridy = 7;
    c.gridheight = 7;
    this.add(sp, c);

And here is the code I use to add the text Areas to the Panel:

title = new JTextField(10);
    author = new JTextField(10);
    dueDate = new JTextField(10);
    setDate = new JTextField(10);
    setWeighting = new JTextField(10);

    c.gridx = 2;
    c.gridy = 1;
    this.add(title, c);//add title field
    c.gridx = 2;
    c.gridy = 2;
    this.add(author, c);//add author field
    c.gridx = 2;
    c.gridy = 3;
    this.add(dueDate, c);//add dueDate field
    c.gridx = 2;
    c.gridy = 4;
    this.add(setDate, c);//add setDate field
    c.gridx = 2;
    c.gridy = 5;
    this.add(setWeighting, c);//add set Weighting field

Answer 1

I was able to partially reproduce your problem like so:

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

public class Foo002 {

   private static final int ROWS = 5;

   private static void createAndShowGui() {
      JPanel assignmentsPanel = new JPanel(new GridBagLayout());
      final JTextArea textarea = new JTextArea(ROWS, 20);

      GridBagConstraints c = new GridBagConstraints();
      int insetGap = 2;
      c.insets = new Insets(insetGap, insetGap, insetGap, insetGap);
      c.fill = GridBagConstraints.HORIZONTAL;
      c.gridwidth = 1;
      c.gridheight = 1;
      c.weightx = 1.0;
      c.weighty = 1.0;
      String[] labels = { "title", "author", "date due", "date set",
            "set weighting" };
      int row = 0;
      for (int i = 0; i < labels.length; i++) {
         JLabel label = new JLabel(labels[i], SwingConstants.CENTER);
         c.gridx = 0;
         c.gridy = i;
         assignmentsPanel.add(label, c);
         c.gridx = 1;
         JTextField textfield = new JTextField(10);
         assignmentsPanel.add(textfield, c);

         label.setPreferredSize(textfield.getPreferredSize());
         row++;
      }
      c.gridx = 0;
      c.gridy = row;
      c.fill = GridBagConstraints.HORIZONTAL;
      Action myAction = new AbstractAction("Fill Area") {

         @Override
         public void actionPerformed(ActionEvent arg0) {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < 10; i++) {
               sb.append("foo bar bif baz spam\n");
            }
            textarea.setText(sb.toString());
         }
      };
      assignmentsPanel.add(new JButton(myAction), c);
      c.gridx = 1;
      assignmentsPanel.add(new JButton("Button 2"), c);
      row++;

      c.gridx = 0;
      c.gridy = row;
      c.gridwidth = 2;
      c.gridheight = ROWS;

      JScrollPane scrollpane = new JScrollPane(textarea);

      assignmentsPanel.add(scrollpane, c);

      JTabbedPane tabbedPanel = new JTabbedPane();
      tabbedPanel.add("Assignments", assignmentsPanel);
      tabbedPanel.add("Modules", new JPanel());

      JOptionPane.showMessageDialog(null, tabbedPanel, "Foo",
            JOptionPane.PLAIN_MESSAGE);

   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

Before and after adding text to JTextArea, it looks like:

And after clicking on tabs:

But it can be fixed by giving the JScrollPane a vertical scrollbar:

  // JScrollPane scrollpane = new JScrollPane(textarea);
  JScrollPane scrollpane = new JScrollPane(textarea,
        JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
        JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);

Which when run looks like:

Looks good on Mac OS, too: