public Boolean isTabClosable( int tabIndex ) {
		JComponent c = (JComponent) getComponentAt( tabIndex );
		Object value = c.getClientProperty( TABBED_PANE_TAB_CLOSABLE );
		return (value instanceof Boolean) ? (boolean) value : isTabsClosable();
	}
Returns whether the tab at the given tab index is closable.
flatlaf-extras/src/main/java/com/formdev/flatlaf/extras/components/FlatTabbedPane.java