Bytecode viewer tools: Jclasslib vs Classfile Inspector.

August 24, 2006

Comparison overview of bytecode viewer applications Jclasslib Bytecode Viewer 3.0 by ej-technologies and Classfile Inspector 2.0 by Industrial Software Technology.


Recently I faced with a need to inspect a Java bytecode in order to create a tests for bytecode processing application. Googling around showed that the market of the bytecode viewers is narrow and actually there is no large variety of possibilities to choose from.

Viewing Java bytecode generated from the Java source is not too common task for most Java developers, so the choice of the tools in this area is quite narrow. In addition to the bytecode viewers discussed here I’ve found the following additional tools:

Feature comparison table

Jclasslib Bytecode Viewer 3.0 Classfile Inspector 2.0
Pricing Free 10€-99€ per license (depends on license amount), free for students and
License GPL Commercial
Supported platforms Windows, Linux, Unix, Mac OS X 10.1/2 Windows, Linux and others (as plugin)
Installation Platform-specific installation package Jar file. Requires write privileges
Available plugins NetBeans module Eclipse 3.1 (and higher) plugin
Standalone version Yes No
Java versions supported 1.5 1.5
Usability Works smoothly Changing default output directory breaks an ability of viewing *.class file corresponding to java source
Presentation Application windows Text file
Bytecode hierarchy presentation Application window “Outline” Eclipse view
Hierarchy link with bytecode editor Yes Yes
Viewing standalone *.class files No Yes
Exploring *.jar files Yes Yes
Binary data presentation No Yes
Bytecode presentation Yes. Separate presentation for each type (methods, fields, exceptions etc.) Yes. All-in-one text file containing binary data, bytecode instruction presentation and source code
Java source presentation No If available in project
Bytecode decompilation No No
Bytecode modification No Yes
Bytecode validation No No
Links inside bytecode Yes No
Export Method bytecode instructions can be copied to clipboard As any text file

Pros and cons

Jclasslib Bytecide Viewer 3.0

  • Availability as a standalone application
  • Links inside bytecode presentation


  • Limited export ability
  • No binary data presentation
  • No source code presentation

Classfile Inspector 2.0

  • Eclipse integration
  • Mixed binary, instructions and java source presentation
  • Bytecode modification


  • No available as standalone application
  • Limited usability


Classfile Inspector 2.0 is a very powerful bytecode viewer application, with good presentation features, giving an ability of inspecting bytecode created by compiler as a derivative of java source code. This provides a user with an opportunity to understand deeply the way bytecode is generated and the affects of different coding decisions on actual code execution. It looks to be an ultimate helper for anyone teaching or studying Java. The main application disadvantage is its tight binding to Eclipse platform, making it almost useless for those working with any other Java IDE.

Jclasslib Bytecide Viewer 3.0 is a good tool for developer that needs just an inspection view on the jar files containing bytecode created, with no ability to modify it or to follow the influence of source code changes on the bytecode generated. Plugins for IDEs other that NetBeans would be nice, even it always can be used as a standalone application.

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