How do I decompile Java class files

Question

What program can I use to decompile a class file  Will I actually get Java code  or is it just JVM assembly code   On Java performance questions on this site I often see responses from people who have  decompiled  the Java class file to see how the compiler optimizes certain things

User · Answer

I use JAD Decompiler   There is an Eclipse plugin for it  jadeclipse  It is pretty nice

User · Answer

Most decompilers for Java are based on JAD   It s a great tool  but unfortunately hasn t been updated for a while and does not handle Java 1 5  classes very well   I have not seen any tools that will properly handle 1 5  classes

User · Answer

There are a few programs you can use  You will get the actual Java code  but sometimes the code will have been obfuscated so methods are named by one letter or number or a random mix of letters and numbers   DJ Decompiler Mocha

User · Answer

I tried several  and Procyon seemed to work the best for me  It s under active development and supports many features of the latest versions of Java   These are the others I tried    CFR   Promising  but often failed method decompilation  I ll be keeping my eye on this one  Also actively developed with support for the latest Java features   Krakatau   Takes a different approach in that it tries to output equivalent Java code instead of trying to reconstruct the original source  which has the potential of making it better for obfuscated code  From my testing it was roughly on par with Procyon  but still nice to have something different  I did have to use the -skip command-line flag so it wouldn t stop on errors  Actively developed  and interestingly enough it s written in Python   JD-GUI   Worked  but Procyon s output was much better  Here s a page comparing Procyon output to the original and JD-GUI  JD-GUI is also available as an Eclipse plugin  which didn t work for me at all  Doesn t seem to be open source and development seems sporadic   JAD   Worked  but only supports Java 1 4 and below  Also available as an Eclipse plugin  No longer under development

User · Answer

Procyon includes a decompiler  It is FOSS

User · Answer

I tried several  and Procyon seemed to work the best for me  It s under active development and supports many features of the latest versions of Java   These are the others I tried    CFR   Promising  but often failed method decompilation  I ll be keeping my eye on this one  Also actively developed with support for the latest Java features   Krakatau   Takes a different approach in that it tries to output equivalent Java code instead of trying to reconstruct the original source  which has the potential of making it better for obfuscated code  From my testing it was roughly on par with Procyon  but still nice to have something different  I did have to use the -skip command-line flag so it wouldn t stop on errors  Actively developed  and interestingly enough it s written in Python   JD-GUI   Worked  but Procyon s output was much better  Here s a page comparing Procyon output to the original and JD-GUI  JD-GUI is also available as an Eclipse plugin  which didn t work for me at all  Doesn t seem to be open source and development seems sporadic   JAD   Worked  but only supports Java 1 4 and below  Also available as an Eclipse plugin  No longer under development

User · Answer

There are a few decompilers out there    A quick search yields    Procyon  open-source  Apache 2  and actively developed Krakatau  open-source  GPLv3  and actively developed CFR  open-source  MIT  and actively developed JAD DJ Java Decompiler Mocha   And many more   These produce Java code  Java comes with something that lets you see JVM byte code  javap

User · Answer

Update February 2016   www javadecompilers com lists JAD as being      the most popular Java decompiler  but primarily of this age only  Written in C    so very fast    Outdated  unsupported and does not decompile correctly Java 5 and later   So your mileage may vary with recent jdk  7  8    The same site list other tools   And javadecompiler  as noted by Salvador Valencia in the comments  Sept 2017   offers a SaaS where you upload the  class file to the cloud and it returns you the decompiled code      Original answer  Oct  2008   The final release of JSR 176  defining the major features of J2SE 5 0  Java SE 5   has been published on September 30  2004  The lastest Java version supported by JAD  the famous Java decompiler written by Mr  Pavel Kouznetsov  is JDK 1 3  Most of the Java decompilers downloadable today from the Internet  such as    DJ Java Decompiler    or    Cavaj Java Decompiler     are powered by JAD  they can not display Java 5 sources    Java Decompiler  Yet another Fast Java decompiler  has    Explicit support for decompiling and analyzing Java 5      class    files  A nice GUI      It works with compilers from JDK 1 1 8 up to JDK 1 7 0  and others  Jikes  JRockit  etc      It features an online live demo version that is actually fully functional  You can just drop a jar file on the page and see the decompiled source code without installing anything

User · Answer

To see Java source code check some decompiler  Go search for jad   If you want to see bytecodes  just use javap which comes with the JDK

User · Answer

There are a few decompilers out there    A quick search yields    Procyon  open-source  Apache 2  and actively developed Krakatau  open-source  GPLv3  and actively developed CFR  open-source  MIT  and actively developed JAD DJ Java Decompiler Mocha   And many more   These produce Java code  Java comes with something that lets you see JVM byte code  javap

User · Answer

All of the JAD links listed so far far seem to be broken  so I found this site  Works great  for Linux  at least   On Ubuntu 11 10 I had to download the static one for whatever reason   http   www varaneckas com jad

User · Answer

Take a look at cavaj

User · Answer

There are a few decompilers out there    A quick search yields    Procyon  open-source  Apache 2  and actively developed Krakatau  open-source  GPLv3  and actively developed CFR  open-source  MIT  and actively developed JAD DJ Java Decompiler Mocha   And many more   These produce Java code  Java comes with something that lets you see JVM byte code  javap

User · Answer

Update February 2016   www javadecompilers com lists JAD as being      the most popular Java decompiler  but primarily of this age only  Written in C    so very fast    Outdated  unsupported and does not decompile correctly Java 5 and later   So your mileage may vary with recent jdk  7  8    The same site list other tools   And javadecompiler  as noted by Salvador Valencia in the comments  Sept 2017   offers a SaaS where you upload the  class file to the cloud and it returns you the decompiled code      Original answer  Oct  2008   The final release of JSR 176  defining the major features of J2SE 5 0  Java SE 5   has been published on September 30  2004  The lastest Java version supported by JAD  the famous Java decompiler written by Mr  Pavel Kouznetsov  is JDK 1 3  Most of the Java decompilers downloadable today from the Internet  such as    DJ Java Decompiler    or    Cavaj Java Decompiler     are powered by JAD  they can not display Java 5 sources    Java Decompiler  Yet another Fast Java decompiler  has    Explicit support for decompiling and analyzing Java 5      class    files  A nice GUI      It works with compilers from JDK 1 1 8 up to JDK 1 7 0  and others  Jikes  JRockit  etc      It features an online live demo version that is actually fully functional  You can just drop a jar file on the page and see the decompiled source code without installing anything

User · Answer

For OSX I recommend  jarzilla or JD-GUI  They both allow you to view jar war etc  file content and decompiles any class files inside of them   Jarzilla  https   code google com p jarzilla  JD-GUI  http   jd benow ca

User · Answer

Here s a list of decompilers as of Feb 2015   Procyon  open-source  https   bitbucket org mstrobel procyon wiki Java 20Decompiler  CFR  free  no source-code available   http   www benf org other cfr   JD  free for non-commercial use only  http   jd benow ca   Fernflower  open-source  https   github com fesh0r fernflower    JAD     given here only for historical reason  Free  no source-code available  http   varaneckas com jad  Outdated  unsupported and does not decompile correctly Java 5 and later   You may test above-mentioned decompilers online  no installation required and make your own educated choice    Java decompilers in the cloud   http   www javadecompilers com

User · Answer

To see Java source code check some decompiler  Go search for jad   If you want to see bytecodes  just use javap which comes with the JDK

User · Answer

On IntelliJ IDEA platform you can use Java Decompiler IntelliJ Plugin  It allows you to display all the Java sources during your debugging process  even if you do not have them all  It is based on the famous tools JD-GUI

User · Answer

For OSX I recommend  jarzilla or JD-GUI  They both allow you to view jar war etc  file content and decompiles any class files inside of them   Jarzilla  https   code google com p jarzilla  JD-GUI  http   jd benow ca

User · Answer

All of the JAD links listed so far far seem to be broken  so I found this site  Works great  for Linux  at least   On Ubuntu 11 10 I had to download the static one for whatever reason   http   www varaneckas com jad

User · Answer

With AndroChef Java Decompiler you can decompile apk  dex  jar and java class-files  It s simple and easy  AndroChef JD is based on FernFlower  You can evaluate it in 10 free uses      AndroChef supports Java language features like generics  enums and annotations  According to some studies  AndroChef Java Decompiler is able to decompile 98 04  of Java applications generated with traditional Java compilers - a very high recovery rate  It is simple but powerful tool that allows you to decompile Java and Dalvik bytecode  DEX  APK  into readable Java source

User · Answer

Update February 2016   www javadecompilers com lists JAD as being      the most popular Java decompiler  but primarily of this age only  Written in C    so very fast    Outdated  unsupported and does not decompile correctly Java 5 and later   So your mileage may vary with recent jdk  7  8    The same site list other tools   And javadecompiler  as noted by Salvador Valencia in the comments  Sept 2017   offers a SaaS where you upload the  class file to the cloud and it returns you the decompiled code      Original answer  Oct  2008   The final release of JSR 176  defining the major features of J2SE 5 0  Java SE 5   has been published on September 30  2004  The lastest Java version supported by JAD  the famous Java decompiler written by Mr  Pavel Kouznetsov  is JDK 1 3  Most of the Java decompilers downloadable today from the Internet  such as    DJ Java Decompiler    or    Cavaj Java Decompiler     are powered by JAD  they can not display Java 5 sources    Java Decompiler  Yet another Fast Java decompiler  has    Explicit support for decompiling and analyzing Java 5      class    files  A nice GUI      It works with compilers from JDK 1 1 8 up to JDK 1 7 0  and others  Jikes  JRockit  etc      It features an online live demo version that is actually fully functional  You can just drop a jar file on the page and see the decompiled source code without installing anything

User · Answer

Procyon includes a decompiler  It is FOSS

User · Answer

JAD doesn t work for me  Ubuntu 11 10 issue  so I ve moved forward and sopped on JODO  At least it has Open Java source code and been able to decompile my  class properly       I recommend to check out  branches generic  branch first  The trunks is not stable

User · Answer

Take a look at cavaj

User · Answer

I use JAD Decompiler   There is an Eclipse plugin for it  jadeclipse  It is pretty nice

User · Answer

To see Java source code check some decompiler  Go search for jad   If you want to see bytecodes  just use javap which comes with the JDK

User · Answer

There are a few programs you can use  You will get the actual Java code  but sometimes the code will have been obfuscated so methods are named by one letter or number or a random mix of letters and numbers   DJ Decompiler Mocha

User · Answer

JD-GUI is really good  You could just open a JAR file and browse through the code as if you are working on an IDE  Good stuff

User · Answer

I use JAD Decompiler   There is an Eclipse plugin for it  jadeclipse  It is pretty nice

User · Answer

There are a few decompilers out there    A quick search yields    Procyon  open-source  Apache 2  and actively developed Krakatau  open-source  GPLv3  and actively developed CFR  open-source  MIT  and actively developed JAD DJ Java Decompiler Mocha   And many more   These produce Java code  Java comes with something that lets you see JVM byte code  javap

User · Answer

Take a look at cavaj

User · Answer

Most decompilers for Java are based on JAD   It s a great tool  but unfortunately hasn t been updated for a while and does not handle Java 1 5  classes very well   I have not seen any tools that will properly handle 1 5  classes

User · Answer

Soot is an option for newer Java code  At least it has the advantage of still being recently maintained     Also  Java Decompiler is a decompiler with both a stand-alone GUI and Eclipse integration   Lastly  Jdec hasn t been mentioned  though it s not as polished as other options

User · Answer

Most decompilers for Java are based on JAD   It s a great tool  but unfortunately hasn t been updated for a while and does not handle Java 1 5  classes very well   I have not seen any tools that will properly handle 1 5  classes

User · Answer

To see Java source code check some decompiler  Go search for jad   If you want to see bytecodes  just use javap which comes with the JDK

User · Answer

There are a few programs you can use  You will get the actual Java code  but sometimes the code will have been obfuscated so methods are named by one letter or number or a random mix of letters and numbers   DJ Decompiler Mocha

User · Answer

On IntelliJ IDEA platform you can use Java Decompiler IntelliJ Plugin  It allows you to display all the Java sources during your debugging process  even if you do not have them all  It is based on the famous tools JD-GUI

User · Answer

Soot is an option for newer Java code  At least it has the advantage of still being recently maintained     Also  Java Decompiler is a decompiler with both a stand-alone GUI and Eclipse integration   Lastly  Jdec hasn t been mentioned  though it s not as polished as other options

User · Answer

JAD is one that works and is simple  Also  if you just want to see the methods  use javap

User · Answer

Most decompilers for Java are based on JAD   It s a great tool  but unfortunately hasn t been updated for a while and does not handle Java 1 5  classes very well   I have not seen any tools that will properly handle 1 5  classes

User · Answer

There are a few programs you can use  You will get the actual Java code  but sometimes the code will have been obfuscated so methods are named by one letter or number or a random mix of letters and numbers   DJ Decompiler Mocha

User · Answer

Here s a list of decompilers as of Feb 2015   Procyon  open-source  https   bitbucket org mstrobel procyon wiki Java 20Decompiler  CFR  free  no source-code available   http   www benf org other cfr   JD  free for non-commercial use only  http   jd benow ca   Fernflower  open-source  https   github com fesh0r fernflower    JAD     given here only for historical reason  Free  no source-code available  http   varaneckas com jad  Outdated  unsupported and does not decompile correctly Java 5 and later   You may test above-mentioned decompilers online  no installation required and make your own educated choice    Java decompilers in the cloud   http   www javadecompilers com

User · Answer

If you want to see how the Java compiler does certain things  you don t want decompilation  you want disassembly  Decompilation involves transforming the bytecode into Java source  meaning that a lot of low level information is lost  and if you re wondering about compiler optimization  this is probably the very information you re interested in   Anyway  I happen to have written an open source Java disassembler  Unlike Javap  this works even on highly pathological classes  so you can see what obfuscation tools are doing to your classes as well  It can also do decompilation  though I wouldn t recommend it

User · Answer

I use JAD Decompiler   There is an Eclipse plugin for it  jadeclipse  It is pretty nice

User · Answer

JAD is one that works and is simple  Also  if you just want to see the methods  use javap

User · Answer

Update February 2016   www javadecompilers com lists JAD as being      the most popular Java decompiler  but primarily of this age only  Written in C    so very fast    Outdated  unsupported and does not decompile correctly Java 5 and later   So your mileage may vary with recent jdk  7  8    The same site list other tools   And javadecompiler  as noted by Salvador Valencia in the comments  Sept 2017   offers a SaaS where you upload the  class file to the cloud and it returns you the decompiled code      Original answer  Oct  2008   The final release of JSR 176  defining the major features of J2SE 5 0  Java SE 5   has been published on September 30  2004  The lastest Java version supported by JAD  the famous Java decompiler written by Mr  Pavel Kouznetsov  is JDK 1 3  Most of the Java decompilers downloadable today from the Internet  such as    DJ Java Decompiler    or    Cavaj Java Decompiler     are powered by JAD  they can not display Java 5 sources    Java Decompiler  Yet another Fast Java decompiler  has    Explicit support for decompiling and analyzing Java 5      class    files  A nice GUI      It works with compilers from JDK 1 1 8 up to JDK 1 7 0  and others  Jikes  JRockit  etc      It features an online live demo version that is actually fully functional  You can just drop a jar file on the page and see the decompiled source code without installing anything

User · Answer

JD-GUI is really good  You could just open a JAR file and browse through the code as if you are working on an IDE  Good stuff

User · Answer

Take a look at cavaj

User · Answer

JAD doesn t work for me  Ubuntu 11 10 issue  so I ve moved forward and sopped on JODO  At least it has Open Java source code and been able to decompile my  class properly       I recommend to check out  branches generic  branch first  The trunks is not stable

User · Answer

If you want to see how the Java compiler does certain things  you don t want decompilation  you want disassembly  Decompilation involves transforming the bytecode into Java source  meaning that a lot of low level information is lost  and if you re wondering about compiler optimization  this is probably the very information you re interested in   Anyway  I happen to have written an open source Java disassembler  Unlike Javap  this works even on highly pathological classes  so you can see what obfuscation tools are doing to your classes as well  It can also do decompilation  though I wouldn t recommend it

User · Answer

With AndroChef Java Decompiler you can decompile apk  dex  jar and java class-files  It s simple and easy  AndroChef JD is based on FernFlower  You can evaluate it in 10 free uses      AndroChef supports Java language features like generics  enums and annotations  According to some studies  AndroChef Java Decompiler is able to decompile 98 04  of Java applications generated with traditional Java compilers - a very high recovery rate  It is simple but powerful tool that allows you to decompile Java and Dalvik bytecode  DEX  APK  into readable Java source

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