How to get a JScrollPane to resize with its parent JPanel

Question

My question is similar to this one (How to get JScrollPanes within a JScrollPane to follow parent's resizing), but that question wasn't clear and the answer there didn't help me..

I have this SSCCE (using MigLayout):

public static final int pref_height = 500;
public static void main(String[] args) {

    JPanel innerPanel = new JPanel(new MigLayout());
    innerPanel.setBorder(new LineBorder(Color.YELLOW, 5));

    for(int i = 0; i < 15; i++) {
        JTextArea textArea = new JTextArea();
        textArea.setColumns(20);
        textArea.setRows(5);
        textArea.setWrapStyleWord(true);
        textArea.setLineWrap(true);
        JScrollPane jsp = new JScrollPane(textArea);

        innerPanel.add(new JLabel("Notes" + i));
        innerPanel.add(jsp, "span, grow");
    }
    JScrollPane jsp = new JScrollPane(innerPanel) {
        @Override
        public Dimension getPreferredSize() {
            setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
            Dimension dim = new Dimension(super.getPreferredSize().width + getVerticalScrollBar().getSize().width, pref_height);
            setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);
            return dim;
        }
    };
    jsp.setBorder(new LineBorder(Color.green, 5));

    JPanel outerPanel = new JPanel();
    outerPanel.setBorder(new LineBorder(Color.RED, 5));
    outerPanel.add(jsp);

    JFrame frame = new JFrame();

    JDesktopPane jdp = new JDesktopPane();
    frame.add(jdp);
    jdp.setPreferredSize(new Dimension(800, 600));
    frame.pack();

    JInternalFrame jif = new JInternalFrame("Title", true, true, true, true);
    jif.pack();
    jif.add(outerPanel);

    jdp.add(jif);
    jif.pack();
    jif.setVisible(true);


    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

I want the JScrollPane to resize whenever the parent JPanel is resized. Basically, I want the green border to line up with the red border. Right now, the green border stays the same size no matter the red border (unless you resize too small).

Answer 1

JPanel outerPanel = new JPanel();

A JPanel uses a FlowLayout by default which always respects the size of the component added to it. As a guess, maybe you can use:

JPanel outerPanel = new JPanel( new BorderLayout() );

A BorderLayout give all the space available to the component added to the panel. By default a JInternalFrame also uses a BorderLayout. So since all the parent components of your scroll pane use a BorderLayout all the space should go to the scroll pane.

When you post a SSCCE you should post code using classes from the JDK that simulates your problem so that everybody can test your SSCCE.