How can I open Java class files in a human-readable way

Question

I m trying to figure out what a Java applet s class file is doing under the hood  Opening it up with Notepad or Textpad just shows a bunch of gobbledy-gook   Is there any way to wrangle it back into a somewhat-readable format so I can try to figure out what it s doing    Environment    Windows w  VS 2008 installed

User · Answer

you can also use the online java decompilers available  For e g  http   www javadecompilers com

User · Answer

If you don t mind reading bytecode  javap should work fine  It s part of the standard JDK installation   Usage  javap  lt options gt   lt classes gt      where options include     -c                        Disassemble the code    -classpath  lt pathlist gt      Specify where to find user class files    -extdirs  lt dirs gt            Override location of installed extensions    -help                     Print this usage message    -J lt flag gt                   Pass  lt flag gt  directly to the runtime system    -l                        Print line number and local variable tables    -public                   Show only public classes and members    -protected                Show protected public classes and members    -package                  Show package protected public classes                              and members  default     -private                  Show all classes and members    -s                        Print internal type signatures    -bootclasspath  lt pathlist gt  Override location of class files loaded                              by the bootstrap class loader    -verbose                  Print stack size  number of locals and args for methods                              If verifying  print reasons for failure

User · Answer

There is no need to decompile Applet class  The public Java API classes sourcecode comes with the JDK  if you choose to install it   and is better readable than decompiled bytecode  You can find compressed in src zip  located in your JDK installation folder

User · Answer

CFR - another java decompiler is a great decompiler for modern Java written i Java 6

User · Answer

what you are looking for is a java de-compiler   I recommend JAD http   www kpdus com jad html  It s free for non commercial use and gets the job done    Note  this isn t going to make the code exactly the same as what was written  i e  you re going to lose comments and possibly variable names  so it s going to be a little bit harder than just reading normal source code     If the developer is really secretive they will have obfuscated their code as well  making it even harder to read

User · Answer

As suggested you can use JAD to decompile it and view the files  To make it easier to read you can use the JADclipse plugin for eclipse to integrate JAD directly to eclipse or use DJ Java Decompiler which is much easier to use than command line JAD

User · Answer

JAD is an excellent option if you want readable Java code as a result   If you really want to dig into the internals of the  class file format though  you re going to want javap   It s bundled with the JDK and allows you to  decompile  the hexadecimal bytecode into readable ASCII   The language it produces is still bytecode  not anything like Java   but it s fairly readable and extremely instructive   Also  if you really want to  you can open up any  class file in a hex editor and read the bytecode directly   The result is identical to using javap

User · Answer

jd-gui is the best decompiler at the moment  it can handle newer features in Java  as compared to the getting-dusty JAD

User · Answer

There is no need to decompile Applet class  The public Java API classes sourcecode comes with the JDK  if you choose to install it   and is better readable than decompiled bytecode  You can find compressed in src zip  located in your JDK installation folder

User · Answer

cpuguru  if your applet has been compiled with javac 1 3  or less   your best option is to use Jad   Unfortunately  the last JDK supported by JAD 1 5 8  Apr 14  2001  is JDK 1 3   If your applet has been compiled with a more recent compiler  you could try JD-GUI   this decompiler is under development  nevertheless  it generates correct Java sources  most of time  for classes compiled with the JDKs 1 4  1 5 or 1 6   DarenW  thank you for your post  JD-GUI is not the best decompiler yet     but I m working on

User · Answer

That s compiled code  you ll need to use a decompiler like JAD  http   www kpdus com jad html

User · Answer

jd-gui is the best decompiler at the moment  it can handle newer features in Java  as compared to the getting-dusty JAD

User · Answer

If the class file you want to look into is open source  you should not decompile it  but instead attach the source files directly into your IDE  that way  you can just view the code of some library class as if it were your own

User · Answer

what you are looking for is a java de-compiler   I recommend JAD http   www kpdus com jad html  It s free for non commercial use and gets the job done    Note  this isn t going to make the code exactly the same as what was written  i e  you re going to lose comments and possibly variable names  so it s going to be a little bit harder than just reading normal source code     If the developer is really secretive they will have obfuscated their code as well  making it even harder to read

User · Answer

cpuguru  if your applet has been compiled with javac 1 3  or less   your best option is to use Jad   Unfortunately  the last JDK supported by JAD 1 5 8  Apr 14  2001  is JDK 1 3   If your applet has been compiled with a more recent compiler  you could try JD-GUI   this decompiler is under development  nevertheless  it generates correct Java sources  most of time  for classes compiled with the JDKs 1 4  1 5 or 1 6   DarenW  thank you for your post  JD-GUI is not the best decompiler yet     but I m working on

User · Answer

jd-gui  http   code google com p innlab downloads detail name jd-gui-0 3 3 windows zip amp can 2 amp q   is the best and user friendly option for decompiling  class file

User · Answer

jd-gui  http   code google com p innlab downloads detail name jd-gui-0 3 3 windows zip amp can 2 amp q   is the best and user friendly option for decompiling  class file

User · Answer

If the class file you want to look into is open source  you should not decompile it  but instead attach the source files directly into your IDE  that way  you can just view the code of some library class as if it were your own

User · Answer

There is no need to decompile Applet class  The public Java API classes sourcecode comes with the JDK  if you choose to install it   and is better readable than decompiled bytecode  You can find compressed in src zip  located in your JDK installation folder

User · Answer

You need to use a decompiler   Others have suggested JAD  there are other options  JAD is the best   I ll echo the comments that you may lose a bit compared to the original source code   It is going to look especially funny if the code used generics  due to erasure

User · Answer

cpuguru  if your applet has been compiled with javac 1 3  or less   your best option is to use Jad   Unfortunately  the last JDK supported by JAD 1 5 8  Apr 14  2001  is JDK 1 3   If your applet has been compiled with a more recent compiler  you could try JD-GUI   this decompiler is under development  nevertheless  it generates correct Java sources  most of time  for classes compiled with the JDKs 1 4  1 5 or 1 6   DarenW  thank you for your post  JD-GUI is not the best decompiler yet     but I m working on

User · Answer

JAD and or JADclipse Eclipse plugin  for sure

User · Answer

There is no need to decompile Applet class  The public Java API classes sourcecode comes with the JDK  if you choose to install it   and is better readable than decompiled bytecode  You can find compressed in src zip  located in your JDK installation folder

User · Answer

As pointed out by  MichaelMyers  use   javap -c  lt name of java class file gt     to get the JVM assembly code  You may also redirect the output to a text file for better visibility   javap -c  lt name of java class file gt   gt  decompiled txt

User · Answer

As suggested you can use JAD to decompile it and view the files  To make it easier to read you can use the JADclipse plugin for eclipse to integrate JAD directly to eclipse or use DJ Java Decompiler which is much easier to use than command line JAD

User · Answer

If the class file you want to look into is open source  you should not decompile it  but instead attach the source files directly into your IDE  that way  you can just view the code of some library class as if it were your own

User · Answer

You want a java decompiler  you can use the command line tool javap to do this   Also  Java Decompiler HOW-TO describes how you can decompile a class file

User · Answer

what you are looking for is a java de-compiler   I recommend JAD http   www kpdus com jad html  It s free for non commercial use and gets the job done    Note  this isn t going to make the code exactly the same as what was written  i e  you re going to lose comments and possibly variable names  so it s going to be a little bit harder than just reading normal source code     If the developer is really secretive they will have obfuscated their code as well  making it even harder to read

User · Answer

You want a java decompiler  you can use the command line tool javap to do this   Also  Java Decompiler HOW-TO describes how you can decompile a class file

User · Answer

You need to use a decompiler   Others have suggested JAD  there are other options  JAD is the best   I ll echo the comments that you may lose a bit compared to the original source code   It is going to look especially funny if the code used generics  due to erasure

User · Answer

As suggested you can use JAD to decompile it and view the files  To make it easier to read you can use the JADclipse plugin for eclipse to integrate JAD directly to eclipse or use DJ Java Decompiler which is much easier to use than command line JAD

User · Answer

Using Jad to decompile it is probably your best option  Unless the code has been obfuscated  it will produce an okay result

User · Answer

JAD and or JADclipse Eclipse plugin  for sure

User · Answer

jd-gui is the best decompiler at the moment  it can handle newer features in Java  as compared to the getting-dusty JAD

User · Answer

If you don t mind reading bytecode  javap should work fine  It s part of the standard JDK installation   Usage  javap  lt options gt   lt classes gt      where options include     -c                        Disassemble the code    -classpath  lt pathlist gt      Specify where to find user class files    -extdirs  lt dirs gt            Override location of installed extensions    -help                     Print this usage message    -J lt flag gt                   Pass  lt flag gt  directly to the runtime system    -l                        Print line number and local variable tables    -public                   Show only public classes and members    -protected                Show protected public classes and members    -package                  Show package protected public classes                              and members  default     -private                  Show all classes and members    -s                        Print internal type signatures    -bootclasspath  lt pathlist gt  Override location of class files loaded                              by the bootstrap class loader    -verbose                  Print stack size  number of locals and args for methods                              If verifying  print reasons for failure

User · Answer

You want a java decompiler  you can use the command line tool javap to do this   Also  Java Decompiler HOW-TO describes how you can decompile a class file

User · Answer

cpuguru  if your applet has been compiled with javac 1 3  or less   your best option is to use Jad   Unfortunately  the last JDK supported by JAD 1 5 8  Apr 14  2001  is JDK 1 3   If your applet has been compiled with a more recent compiler  you could try JD-GUI   this decompiler is under development  nevertheless  it generates correct Java sources  most of time  for classes compiled with the JDKs 1 4  1 5 or 1 6   DarenW  thank you for your post  JD-GUI is not the best decompiler yet     but I m working on

User · Answer

You want a java decompiler  you can use the command line tool javap to do this   Also  Java Decompiler HOW-TO describes how you can decompile a class file

User · Answer

JAD is an excellent option if you want readable Java code as a result   If you really want to dig into the internals of the  class file format though  you re going to want javap   It s bundled with the JDK and allows you to  decompile  the hexadecimal bytecode into readable ASCII   The language it produces is still bytecode  not anything like Java   but it s fairly readable and extremely instructive   Also  if you really want to  you can open up any  class file in a hex editor and read the bytecode directly   The result is identical to using javap

User · Answer

That s compiled code  you ll need to use a decompiler like JAD  http   www kpdus com jad html

User · Answer

If the class file you want to look into is open source  you should not decompile it  but instead attach the source files directly into your IDE  that way  you can just view the code of some library class as if it were your own

User · Answer

you can also use the online java decompilers available  For e g  http   www javadecompilers com

User · Answer

You need to use a decompiler   Others have suggested JAD  there are other options  JAD is the best   I ll echo the comments that you may lose a bit compared to the original source code   It is going to look especially funny if the code used generics  due to erasure

User · Answer

JAD and or JADclipse Eclipse plugin  for sure

User · Answer

Using Jad to decompile it is probably your best option  Unless the code has been obfuscated  it will produce an okay result

User · Answer

As suggested you can use JAD to decompile it and view the files  To make it easier to read you can use the JADclipse plugin for eclipse to integrate JAD directly to eclipse or use DJ Java Decompiler which is much easier to use than command line JAD

User · Answer

what you are looking for is a java de-compiler   I recommend JAD http   www kpdus com jad html  It s free for non commercial use and gets the job done    Note  this isn t going to make the code exactly the same as what was written  i e  you re going to lose comments and possibly variable names  so it s going to be a little bit harder than just reading normal source code     If the developer is really secretive they will have obfuscated their code as well  making it even harder to read

User · Answer

Using Jad to decompile it is probably your best option  Unless the code has been obfuscated  it will produce an okay result

User · Answer

Using Jad to decompile it is probably your best option  Unless the code has been obfuscated  it will produce an okay result

User · Answer

JAD and or JADclipse Eclipse plugin  for sure

User · Answer

CFR - another java decompiler is a great decompiler for modern Java written i Java 6

User · Answer

JAD is an excellent option if you want readable Java code as a result   If you really want to dig into the internals of the  class file format though  you re going to want javap   It s bundled with the JDK and allows you to  decompile  the hexadecimal bytecode into readable ASCII   The language it produces is still bytecode  not anything like Java   but it s fairly readable and extremely instructive   Also  if you really want to  you can open up any  class file in a hex editor and read the bytecode directly   The result is identical to using javap

User · Answer

That s compiled code  you ll need to use a decompiler like JAD  http   www kpdus com jad html

User · Answer

If you don t mind reading bytecode  javap should work fine  It s part of the standard JDK installation   Usage  javap  lt options gt   lt classes gt      where options include     -c                        Disassemble the code    -classpath  lt pathlist gt      Specify where to find user class files    -extdirs  lt dirs gt            Override location of installed extensions    -help                     Print this usage message    -J lt flag gt                   Pass  lt flag gt  directly to the runtime system    -l                        Print line number and local variable tables    -public                   Show only public classes and members    -protected                Show protected public classes and members    -package                  Show package protected public classes                              and members  default     -private                  Show all classes and members    -s                        Print internal type signatures    -bootclasspath  lt pathlist gt  Override location of class files loaded                              by the bootstrap class loader    -verbose                  Print stack size  number of locals and args for methods                              If verifying  print reasons for failure

User · Answer

That s compiled code  you ll need to use a decompiler like JAD  http   www kpdus com jad html

User · Answer

JAD is an excellent option if you want readable Java code as a result   If you really want to dig into the internals of the  class file format though  you re going to want javap   It s bundled with the JDK and allows you to  decompile  the hexadecimal bytecode into readable ASCII   The language it produces is still bytecode  not anything like Java   but it s fairly readable and extremely instructive   Also  if you really want to  you can open up any  class file in a hex editor and read the bytecode directly   The result is identical to using javap

User · Answer

If you don t mind reading bytecode  javap should work fine  It s part of the standard JDK installation   Usage  javap  lt options gt   lt classes gt      where options include     -c                        Disassemble the code    -classpath  lt pathlist gt      Specify where to find user class files    -extdirs  lt dirs gt            Override location of installed extensions    -help                     Print this usage message    -J lt flag gt                   Pass  lt flag gt  directly to the runtime system    -l                        Print line number and local variable tables    -public                   Show only public classes and members    -protected                Show protected public classes and members    -package                  Show package protected public classes                              and members  default     -private                  Show all classes and members    -s                        Print internal type signatures    -bootclasspath  lt pathlist gt  Override location of class files loaded                              by the bootstrap class loader    -verbose                  Print stack size  number of locals and args for methods                              If verifying  print reasons for failure

User · Answer

jd-gui is the best decompiler at the moment  it can handle newer features in Java  as compared to the getting-dusty JAD

User · Answer

As pointed out by  MichaelMyers  use   javap -c  lt name of java class file gt     to get the JVM assembly code  You may also redirect the output to a text file for better visibility   javap -c  lt name of java class file gt   gt  decompiled txt

User · Answer

You need to use a decompiler   Others have suggested JAD  there are other options  JAD is the best   I ll echo the comments that you may lose a bit compared to the original source code   It is going to look especially funny if the code used generics  due to erasure

[java] How can I open Java .class files in a human-readable way?

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