JFrame doesn't add TabbedPane

My JFrame is not adding the JTabbedPane & I don’t know if the crash is some sort of bug of my eclipse. There are no syntaxes errors or anything that seems to be to me wrong. Could anyone else try to run it & see if it works? The code is already ready to run. Thanks in advance

You’ve added JMenuBar in Content pane. It is not required.

remove this line in your code mainFrame.add(bar); & mainFrame.setJMenuBar(bar); is already added.