I was browsing the docs recently, and I noticed that many
swing classes don't have an @since tag indicating which
release they were introduced in.

Examples: JComponent, javax.swing.Timer

It turns out that unless otherwise stated, Swing classes
are considered to have been added to the public core in 1.2.

We should add a note to the package documentation to say so.
It would let developers know how old various swing classes are,
and give them a baseline for the APIs in those classes.