Looking for help building 'rhdb-explain' Visual Explain tool

I'm hoping there's someone here with experience in building the Visual
Explain tool from Red Hat. I downloaded it and the J2 SDK, but when I
attempt to follow the build instructions, I get messages like:

error: Type `JTableHeader' not found in the declaration of the local
variable `header'.
    [javac]             JTableHeader header = null;

To me, this indicates that the SDK isn't installed (properly). But I
admit I'm pretty much a Java know-nothin'.