According to Swing tutorial:
Some Swing component methods are labelled \"thread safe\" in the API specification; these can be safely invoked from any
For a list of classes with the comment in the javadocs & src files "is thread safe" returns the following
JEditorPane
JTextArea
AbstractDocument
DefaultCaret
DefaultStyledDocument
JTextComponent
PlainDocument
StyleContext
HTMLDocument
UndoManager
This is not saying that there are others documented or undocumented within the src that are thread safe.
It strikes me as a rather strange question but I would treat most components as not being threadsafe and since Swing is a single threaded model and all updates need to happen on the event dispatcher thread this is pretty easy to do.