Jlint will check your Java code and find bugs, inconsistencies and synchronization problems by doing data flow analysis on the code and building the lock graph. Jlint is fast, easy to learn, and requires no changes in the class files to be checked.
FProfiler is a Java Profiler using log4j. Its very fast because it inserts the needed instructions into the byte-code of the class. It can be used to find "Hotspots" in Java programs, libs and servlet environments simply every Java class.