Unable to add to JFrame after removeAll()

Question

I have a relatively small class called "LoadingWindow" this class has a constructor that calls a Initialize function to setup the frame. Not I was testing some things to try to solve why it would not update. While testing I added "this.removeAll();" to the head of the initialize method. Turns out, I cant add anything after that. Anything I add, simply will not show.

Here is a slightly trimmed down version of the class:

public class LoadingWindow extends JFrame{

public JPanel panel;

public JProgressBar bar;

private JLabel label;

public LoadingWindow()
{

    this.Initialize();

}

public void Initialize()
{
    this.removeAll();

    this.setSize(300, 150);

    panel = new JPanel(new BorderLayout());
    bar = new JProgressBar(0,100);
    label = new JLabel("Please remain calm, we're just loading...");

    panel.add(bar,BorderLayout.CENTER);
    panel.add(label,BorderLayout.SOUTH);

    this.add(panel);

    this.validate();
    this.repaint();
    this.setVisible(true);
}
}

The window itself does pop up properly, with a title. However the window itself is completely blank.

I implement this class statically so that four other objects can access it in the EditorPanel class. Its defined as:

public static LoadingWindow loadingWindow;

and initialized in the constructor with:

loadingWindow = new LoadingWindow();

There is then a double check within the functions that use it to show it if it is hidden.

if(!EditorPanel.loadingWindow.isVisible()){EditorPanel.loadingWindow.Initialize();}

Overall I'm a bit confused as to why no content is showing, and I am very interested in any questions asked, and am willing to provide any info necessary. Google didn't provide a whole lot, and every answer I found I had already implemented "such as repaint and validate".

I look forward to hearing from you!

~Travis

Answer 1

removeAll() as said by @TomHawtintackline (+1 to him), is not forwarded to the JFrames contentPane; like add(), remove() or setLayout() is.

Thus when you do JFrame#removeAll() it removes the root pane of JFrame. See How to Use Root Panes for an interesting read and may prove fruitful for future endeavors.

You should do:

getContentPane().removeAll();// will make sure we remove all components from the contentPane

• Also dont extend JFrame unnecessarily (unless adding functionality beyond its current capability) rather just create an instance of JFrame and use that

• Dont call setSize rather use an appropriate LayoutManager and/or override getPreferredSize() of JPanel and return dimensions which fit drawings, thus you can call pack() on JFrame before setting it visible.

• I see no need for validate() and repaint() these should only be called when a component is added to a visible container. Even than rather do revalidate() which will work for adding and removing a component (it inturn calls validate())