How to find unused/dead code in java projects

Question

What tools do you use to find unused/dead code in large java projects? Our product has been in development for some years, and it is getting very hard to manually detect code that is no longer in use. We do however try to delete as much unused code as possible.

Suggestions for general strategies/techniques (other than specific tools) are also appreciated.

Edit: Note that we already use code coverage tools (Clover, IntelliJ), but these are of little help. Dead code still has unit tests, and shows up as covered. I guess an ideal tool would identify clusters of code which have very little other code depending on it, allowing for docues manual inspection.

Answer 1

• FindBugs is excellent for this sort of thing.
• PMD (Project Mess Detector) is another tool that can be used.

However, neither can find public static methods that are unused in a workspace. If anyone knows of such a tool then please let me know.

Answer 2

IntelliJ has code analysis tools for detecting code which is unused. You should try making as many fields/methods/classes as non-public as possible and that will show up more unused methods/fields/classes

I would also try to locate duplicate code as a way of reducing code volume.

My last suggestion is try to find open source code which if used would make your code simpler.

Answer 3

The Structure101 slice perspective will give a list (and dependency graph) of any "orphans" or "orphan groups" of classes or packages that have no dependencies to or from the "main" cluster.

Answer 4

I use Doxygen to develop a method call map to locate methods that are never called. On the graph you will find islands of method clusters without callers. This doesn't work for libraries since you need always start from some main entry point.

Answer 5

CodePro was recently released by Google with the Eclipse project. It is free and highly effective. The plugin has a 'Find Dead Code' feature with one/many entry point(s). Works pretty well.

Answer 6

I'm suprised ProGuard hasn't been mentioned here. It's one of the most mature products around.

ProGuard is a free Java class file shrinker, optimizer, obfuscator, and preverifier. It detects and removes unused classes, fields, methods, and attributes. It optimizes bytecode and removes unused instructions. It renames the remaining classes, fields, and methods using short meaningless names. Finally, it preverifies the processed code for Java 6 or for Java Micro Edition.

Some uses of ProGuard are:

• Creating more compact code, for smaller code archives, faster transfer across networks, faster loading, and smaller memory footprints.
• Making programs and libraries harder to reverse-engineer.
• Listing dead code, so it can be removed from the source code.
• Retargeting and preverifying existing class files for Java 6 or higher, to take full advantage of their faster class loading.

Here example for list dead code: https://www.guardsquare.com/en/products/proguard/manual/examples#deadcode