100 by 200 is not wide enough for the title bar, so I bumped it up to 200x200. Using that code my window's content pane is 202 pixels in both directions, and the content pane doesn't know how large it is when it's initialized.
The way my game works is that I each menu screen or gameplay screen is a different JPanel, and I switch the current ContentPane in the JPanel to the appropriate game screen. One of these JPanels needs to know it's own size
I can throw in a hack where I have a public variable in the JFrame that represents the intended size and then have the ContentPane use that in place of getHeight and getWidth, but that doesn't seem like a good solution.