Bug 81983 [preferences] Disabling and enabling folding on small file takes forever
3.1 M4 Using enable/disable folding on a small CU takes forever. This is caused by the recent change to apply the preference to all Java editors. In another (hidden) window (Debug) I had StyledText open which (understandably) took long to react on the preference change. Non-visible editor's should not react to this change until they become visible.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/JavaEditor.java
protected JavaWordIterator fIterator= new JavaWordIterator();
		/**
		 * Creates a new next sub-word action.
		 * 
		 * @param code Action code for the default operation. Must be an action code from @see org.eclipse.swt.custom.ST.
		 */
		protected NextSubWordAction(int code) {
			super(getSourceViewer().getTextWidget(), code);
		}
		/*
		 * @see org.eclipse.jface.action.IAction#run()
		 */
		public void run() {
			
			final IPreferenceStore store= getPreferenceStore();
			if (!store.getBoolean(PreferenceConstants.EDITOR_SUB_WORD_NAVIGATION)) {
				super.run();
				return;				
			}
			
			final ISourceViewer viewer= getSourceViewer();
			final IDocument document= viewer.getDocument();
			fIterator.setText((CharacterIterator) new DocumentCharacterIterator(document));