SwingUtilities.updateComponentTreeUI(this); will reset your own UI, if you call setUI() in constructor.

Example:

PeterCustomeTabbedPane —– extend ——> MaryCustomTabbedPane —-  extend ->   JTabbedPane (swing component)

Suppose PeterCustomeTabbedPane and MaryCustomTabbedPane have their own TabbedPaneUI, once you called SwingUtilities.updateComponentTreeUI(this); , PeterCustomeTabbedPane’s UI class will be reset to MaryCustomTabbedPane’s UI class.

Workaround:

!!! dont call setUI in PeterCustomeTabbedPane, override the setUI() method and set whatever you want to UI.