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

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In theory  you can t deterministically find unused code   Theres a mathematical proof of this  well  this is a special case of a more general theorem    If you re curious  look up the Halting Problem   This can manifest itself in Java code in many ways    Loading classes based on user input  config files  database entries  etc  Loading external code  Passing object trees to third party libraries  etc    That being said  I use IDEA IntelliJ as my IDE of choice and it has extensive analysis tools for findign dependencies between modules  unused methods  unused members  unused classes  etc   Its quite intelligent too like a private method that isn t called is tagged unused but a public method requires more extensive analysis

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Eclipse can show highlight code that can t be reached  JUnit can show you code coverage  but you d need some tests and have to decide if the relevant test is missing or the code is really unused

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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

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One thing I ve been known to do in Eclipse  on a single class  is change all of its methods to private and then see what complaints I get   For methods that are used  this will provoke errors  and I return them to the lowest access level I can   For methods that are unused  this will provoke warnings about unused methods  and those can then be deleted   And as a bonus  you often find some public methods that can and should be made private   But it s very manual

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In Eclipse Goto Windows   Preferences   Java   Compiler   Errors Warnings and change all of them to errors  Fix all the errors  This is the simplest way  The beauty is that this will allow you to clean up the code as you write   Screenshot Eclipse Code

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We ve started to use Find Bugs to help identify some of the funk in our codebase s target-rich environment for refactorings  I would also consider Structure 101 to identify spots in your codebase s architecture that are too complicated  so you know where the real swamps are

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Netbeans  here is a plugin for Netbeans dead code detector    It would be better if it could link to and highlight the unused code  You can vote and comment here  Bug 181458 - Find unused public classes  methods  fields

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An Eclipse plugin that works reasonably well is Unused Code Detector   It processes an entire project  or a specific file and shows various unused dead code methods  as well as suggesting visibility changes  i e  a public method that could be protected or private

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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

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I would instrument the running system to keep logs of code usage  and then start inspecting code that is not used for months or years   For example if you are interested in unused classes  all classes could be instrumented to log when instances are created  And then a small script could compare these logs against the complete list of classes to find unused classes   Of course  if you go at the method level you should keep performance in mind  For example  the methods could only log their first use  I dont know how this is best done in Java  We have done this in Smalltalk  which is a dynamic language and thus allows for code modification at runtime  We instrument all methods with a logging call and uninstall the logging code after a method has been logged for the first time  thus after some time no more performance penalties occur  Maybe a similar thing can be done in Java with static boolean flags

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I found Clover coverage tool which instruments code and highlights the code that is used and that is unused  Unlike Google CodePro Analytics  it also works for WebApplications  as per my experience and I may be incorrect about Google CodePro     The only drawback that I noticed is that it does not takes Java interfaces into account

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User coverage tools  such as EMMA  But it s not static tool  i e  it requires to actually run the application through regression testing  and through all possible error cases  which is  well  impossible       Still  EMMA is very useful

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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

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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

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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

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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

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Code coverage tools  such as Emma  Cobertura  and Clover  will instrument your code and record which parts of it gets invoked by running a suite of tests  This is very useful  and should be an integral part of your development process  It will help you identify how well your test suite covers your code   However  this is not the same as identifying real dead code  It only identifies code that is covered  or not covered  by tests  This can give you false positives  if your tests do not cover all scenarios  as well as false negatives  if your tests access code that is actually never used in a real world scenario    I imagine the best way to really identify dead code would be to instrument your code with a coverage tool in a live running environment and to analyse code coverage over an extended period of time    If you are runnning in a load balanced redundant environment  and if not  why not   then I suppose it would make sense to only instrument one instance of your application and to configure your load balancer such that a random  but small  portion of your users run on your instrumented instance  If you do this over an extended period of time  to make sure that you have covered all real world usage scenarios - such seasonal variations   you should be able to see exactly which areas of your code are accessed under real world usage and which parts are really never accessed and hence dead code    I have never personally seen this done  and do not know how the aforementioned tools can be used to instrument and analyse code that is not being invoked through a test suite - but I am sure they can be

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Use a test coverage tool to instrument your codebase  then run the application itself  not the tests    Emma and Eclemma will give you nice reports of what percentage of what classes are run for any given run of the code

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Code coverage tools  such as Emma  Cobertura  and Clover  will instrument your code and record which parts of it gets invoked by running a suite of tests  This is very useful  and should be an integral part of your development process  It will help you identify how well your test suite covers your code   However  this is not the same as identifying real dead code  It only identifies code that is covered  or not covered  by tests  This can give you false positives  if your tests do not cover all scenarios  as well as false negatives  if your tests access code that is actually never used in a real world scenario    I imagine the best way to really identify dead code would be to instrument your code with a coverage tool in a live running environment and to analyse code coverage over an extended period of time    If you are runnning in a load balanced redundant environment  and if not  why not   then I suppose it would make sense to only instrument one instance of your application and to configure your load balancer such that a random  but small  portion of your users run on your instrumented instance  If you do this over an extended period of time  to make sure that you have covered all real world usage scenarios - such seasonal variations   you should be able to see exactly which areas of your code are accessed under real world usage and which parts are really never accessed and hence dead code    I have never personally seen this done  and do not know how the aforementioned tools can be used to instrument and analyse code that is not being invoked through a test suite - but I am sure they can be

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DCD is not a plugin for some IDE but can be run from ant or standalone  It looks like a static tool and it can do what PMD and FindBugs can t  I will try it   P S  As mentioned in a comment below  the Project lives now in GitHub

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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

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There is a Java project - Dead Code Detector  DCD   For source code it doesn t seem to work well  but for  jar file - it s really good  Plus you can filter by class and by method

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There are tools which profile code and provide code coverage data  This lets you see  as code is run  how much of it is being called  You can get any of these tools to find out how much orphan code you have

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One thing I ve been known to do in Eclipse  on a single class  is change all of its methods to private and then see what complaints I get   For methods that are used  this will provoke errors  and I return them to the lowest access level I can   For methods that are unused  this will provoke warnings about unused methods  and those can then be deleted   And as a bonus  you often find some public methods that can and should be made private   But it s very manual

[java] How to find unused/dead code in java projects

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