Why? java.awt.AWTError: BoxLayout can't be shared

[toratora]

Below is my code. I got "java.awt.AWTError: BoxLayout can't be shared" error. But it's fine

if I replace the line 5 with
frame.setLayout(new BoxLayout(pane, BoxLayout.Y_AXIS));

Although I can pinpoint the location of error and fix it up, I don't know why this error happen.


public class BoxLayoutDemo {
public BoxLayoutDemo(){
JFrame frame = new JFrame("Button Demo");
Container pane = frame.getContentPane();
frame.setLayout(new BoxLayout(frame, BoxLayout.Y_AXIS));

JButton button1 = new JButton ("I Love You");
pane.add(button1);

frame.pack();
frame.setVisible(true);
}
public static void main (String[] args){
new BoxLayoutDemo();
}
}

[IceCubeC]

a layout manager determines the size and position of the components within a container or panel, but has nothing to do with a JFrame

a JFrame is simply used as top-level window with a title and a border