jclasslib is an open source Java bytecode viewer
Editor: jclasslib bytecode Viewer is a tool that visualizes all aspects of compiled Java class files and the contained bytecode. In addition, it contains a library that enables developers to read, modify and write Java class files and bytecode.

This release brings full compatibility with Java 1.5 (list of changes in the class file format)
Displays new access flags in Java 1.5:
ACC_ENUM
ACC_ANNOTATION
ACC_BRIDGE
ACC_VARARGS
Displays new attributes in Java 1.5:
RuntimeVisibleAnnotations
RuntimeInvisibleAnnotations
RuntimeVisibleParameterAnnotations
RuntimeInvisibleParameterAnnotations
EnclosingMethod
Signature
LocalVariableTypeTable
Various bugfixes in the GUI you can free download jclasslib for unix 3.0 now.