How to have a JButton that moves as I scroll on the frame?

Question

I have a Panel which I have made scrollable in my frame. What I need is to add a button that stays fixed in the lower right corner even when I scroll. I'm new to Java Swing so would appreciate all and any help that I can get.

mainPanel = new SimulationPanel(); //class SimulationPanel extends JPanel

//making mainPanel scrollable
mainPanel.setPreferredSize(new Dimension(((int)(WIDTH*1.2)), HEIGHT));
JScrollPane scrollPane = new JScrollPane(mainPanel);
scrollPane.setViewportView(mainPanel);

// Settings for JFrame
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
frame = new JFrame("Warehouse Simulator");
frame.setContentPane(scrollPane);
frame.setSize(screenSize.width, screenSize.height);
frame.setResizable(true);
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.setVisible(true);

Answer 1

I would use nested panels with the outer one be with BorderLayout . Then one with FlowLayout and align FlowLayout.RIGHT and the button inside it.

public class Example extends JFrame {
    public Example() {
        super("");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        setLayout(new BorderLayout());

        JTextArea textArea = new JTextArea(10000, 0);
        JScrollPane scrollPane = new JScrollPane(textArea);

        add(scrollPane, BorderLayout.CENTER);

        JButton button = new JButton("button");

        JPanel panelWithButton = new JPanel(new FlowLayout(FlowLayout.RIGHT));
        panelWithButton.add(button);
        add(panelWithButton, BorderLayout.PAGE_END);

        setLocationByPlatform(true);
        pack();
        setSize(600, 600);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            new Example().setVisible(true);
        });
    }
}

Result:

Answer 2

I would go for a BoxLayout. Add another panel (metaPanel) in which your first put your scrollingPanel, and then you add a button. Instead of usgin scrollingPanel as contentPane, you use metaPanel. Example (the example works, but you need to modify it to make the interface look nice):

    JPanel mainPanel = new JPanel();
    JScrollPane scrollPane = new JScrollPane(mainPanel);
    scrollPane.setViewportView(mainPanel);

    JPanel metaPanel = new JPanel();
    BoxLayout boxlayout = new BoxLayout(metaPanel, BoxLayout.Y_AXIS);
    metaPanel.setLayout(boxlayout);
    metaPanel.add(scrollPane);
    metaPanel.add(new JButton("button"));

    // Settings for JFrame
    frame = new JFrame("Warehouse Simulator");
    frame.setContentPane(metaPanel); // Put metaPanel here
    frame.setSize(500, 300);
    frame.setResizable(true);
    frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    frame.setVisible(true);