Not many people know this, so a little background.... There are many possible ways to build a JDK -- debug, fastdebug, product, etc. When Sun ships a JDK, it is the product version (I believe they use to ship the debug version too -- java_g).
In my case, I work for a company that licensed and creates our own version of the JVM. So, we build our own JDK binaries from the modified Sun source. And for
testing purposes, I generally test with the debug JVM. The debug version has all the symbols (-g) and all assertions turned on.
I don't think Sun ships the debug version anymore. If you want that, you'll have to compile it from the JDK source.
Henry