Disposing of GUI Elements

Question

I have several GUI elements added to a JPanel. The JPanel is added to a JScrollPane. The JScrollPane is added to a JFrame (CENTER section of a BorderLayout).

At times I need to remove the JScrollPane and make the space available for other elements. I've provided a method for that. Want to make sure that this method disposes of all resources used by the old JScrollPane and makes them available for Garbage Collection. Please see code below. Is my clearCenter() method sufficient for this task? Is there a better way to do it?

Thanks.

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

public class MyGui extends JFrame {
    private JScrollPane scroll;
    private JPanel panel;
    private JButton button1;
    private JButton button2;
    private JButton button3;
    private JButton button4;

    // Constructor
    public MyGui() {
        super("Playback");
        setSize(250, 200);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        BorderLayout layout = new BorderLayout();
        setLayout(layout);

        panel = new JPanel();
        GridLayout grid = new GridLayout(0, 1, 30, 30);
        panel.setLayout(grid);

        button1 = new JButton("Button1");
        button2 = new JButton("Button2");
        button3 = new JButton("Button3");
        button4 = new JButton("Button4");
        panel.add(button1);
        panel.add(button2);
        panel.add(button3);
        panel.add(button4);

        scroll = new JScrollPane(panel,
                JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        add(scroll, BorderLayout.CENTER);
        add(new JLabel("South", JLabel.CENTER),BorderLayout.SOUTH);
        add(new JLabel("North", JLabel.CENTER),BorderLayout.NORTH);
        add(new JLabel("East", JLabel.CENTER),BorderLayout.EAST);
        add(new JLabel("West", JLabel.CENTER),BorderLayout.WEST);
        setVisible(true);
    }

    public void clearCenter() {
        button1 = null;
        button2 = null;
        button3 = null;
        button4 = null;
        panel = null;
        remove(scroll);
        scroll =  null;
    }

}

Answer 1

At times I need to remove the JScrollPane and make the space available for other elements.

Use a CardLayout as shown in this answer. And I would not worry too much about disposing of a scroll pane, keep it in memory. When it is next needed, update the scroll pane contents then flip back to that card in the layout.

Resetting the content of the scroll-pane can be done like below. Activate the first button to see the button panel replaced by the yellow panel as the view of the scroll-pane. Note that this code is a 'ready to run' MCVE (with a main(String[]) to show it onscreen). Please post MCVE code in future.

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

public class MyGui extends JFrame {

    private JScrollPane scroll;
    private JPanel panel;
    private JPanel brightPanel;
    private JButton button1;
    private JButton button2;
    private JButton button3;
    private JButton button4;

    // Constructor
    public MyGui() {
        super("Playback");
        setSize(250, 200);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        BorderLayout layout = new BorderLayout();
        setLayout(layout);

        // create the panel, but don't add it yet.
        brightPanel = new JPanel();
        brightPanel.setBackground(Color.YELLOW);

        panel = new JPanel();
        GridLayout grid = new GridLayout(0, 1, 30, 30);
        panel.setLayout(grid);

        button1 = new JButton("Button1");
        button2 = new JButton("Button2");
        button3 = new JButton("Button3");
        button4 = new JButton("Button4");
        panel.add(button1);
        panel.add(button2);
        panel.add(button3);
        panel.add(button4);

        ActionListener listener = new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                changeViews();
            }
        };
        button1.addActionListener(listener);

        scroll = new JScrollPane(panel,
                JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        add(scroll, BorderLayout.CENTER);
        add(new JLabel("South", JLabel.CENTER), BorderLayout.SOUTH);
        add(new JLabel("North", JLabel.CENTER), BorderLayout.NORTH);
        add(new JLabel("East", JLabel.CENTER), BorderLayout.EAST);
        add(new JLabel("West", JLabel.CENTER), BorderLayout.WEST);
        setVisible(true);
    }

    public void changeViews() {
        scroll.setViewportView(brightPanel);
    }

    public static void main(String[] args) {
        Runnable r = new Runnable() {

            @Override
            public void run() {
                new MyGui();
            }
        };
        SwingUtilities.invokeLater(r);
    }
}