Simple JDB Debugging Lessons
You will need Java and the JDK toolkit to use the Java Debugger. Installation instructions for Mac can be found here...
http://www.java.com/en/download/help/mac_install.xml
Linux users can intall it via their package manager.
For official JDB documentation please refer to the the Oracle page below...
http://docs.oracle.com/javase/7/docs/technotes/tools/solaris/jdb.html