Using the same JToolBar on 2 different JFrames - jframe

Question

This example creates the ToolBar and attempts to add the same ToolBar to 2 different JFrames.
I was expecting that both JFrames would have the identical ToolBar, but apparently the ToolBar is being added only to the 2nd JFrame.
If the code for the 2nd JFrame is commented out then the ToolBar gets added to the 1st Frame as expected.
import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.Dimension;
import javax.swing.*;
public class ToolBarSample {
public static void main(final String args[]) {
JFrame frame = new JFrame("JToolBar Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JToolBar toolbar = new JToolBar();
toolbar.setRollover(true);
JButton button = new JButton("button");
toolbar.add(button);
toolbar.addSeparator();
toolbar.add(new JButton("button 2"));
toolbar.add(new JButton("button 3"));
toolbar.add(new JButton("button 4"));
Container contentPane = frame.getContentPane();
contentPane.add(toolbar, BorderLayout.NORTH);
contentPane.setPreferredSize(new Dimension(10,10));
JTextArea textArea = new JTextArea();
JScrollPane pane = new JScrollPane(textArea);
contentPane.add(pane, BorderLayout.CENTER);
frame.setSize(500, 500);
frame.setVisible(true);
JFrame frame2 = new JFrame("JToolBar Example 2");
frame2.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container contentPane2 = frame2.getContentPane();
contentPane2.add(toolbar, BorderLayout.NORTH);
frame2.setSize(500, 500);
frame2.setVisible(true);
}
}
Why is the JToolBar only being added to the 2nd JFrame and not both?

Answer 1

You can add a JToolbar (Component) into only 1 JFrame (Container) at the same time. Because Swing/AWT component's struct is a tree. A tree's node can not have more than 1 parent.
In your case, you can implement a method to create a JToolbar. Then, you create 2 JToolbar and add to 2 JFrame as follows:
class ToolBarSample {
public static void main(final String args[]) {
JFrame frame = new JFrame("JToolBar Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container contentPane = frame.getContentPane();
contentPane.add(createToolbar(), BorderLayout.NORTH);
contentPane.setPreferredSize(new Dimension(10, 10));
JTextArea textArea = new JTextArea();
JScrollPane pane = new JScrollPane(textArea);
contentPane.add(pane, BorderLayout.CENTER);
frame.setSize(500, 500);
frame.setVisible(true);
JFrame frame2 = new JFrame("JToolBar Example 2");
frame2.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container contentPane2 = frame2.getContentPane();
contentPane2.add(createToolbar(), BorderLayout.NORTH);
frame2.setSize(500, 500);
frame2.setVisible(true);
}
private static JToolBar createToolbar() {
JToolBar toolbar = new JToolBar();
toolbar.setRollover(true);
JButton button = new JButton("button");
toolbar.add(button);
toolbar.addSeparator();
toolbar.add(new JButton("button 2"));
toolbar.add(new JButton("button 3"));
toolbar.add(new JButton("button 4"));
return toolbar;
}
}