I have a java class file. How do I find out the version of the compiler used to compile this file? I'm on Ubuntu Server 12.04.


The JDK includes a javap command. It gives a lot information, but you can use it like this:

javap -verbose yourClass | grep version

Example output:

  minor version: 0
  major version: 51

The major version tells you which version the compiler had:

J2SE 8 = 52,
J2SE 7 = 51,
J2SE 6.0 = 50,
J2SE 5.0 = 49,
JDK 1.4 = 48,
JDK 1.3 = 47,
JDK 1.2 = 46,
JDK 1.1 = 45
  • for 45, the exact compiler version depends on the minor version. 45.3 would be 1.0.2 I beleive. – Antimony Apr 15 '13 at 17:13
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    This answer should have been the accepted one: javap works on Windows AND Linux. – avgvstvs Apr 18 '14 at 13:56
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    This actually tells you the version of the class file format, not the version of the compiler or other tool used to generate it. javac supports the -target or --release flag to generate class files targeted at earlier versions of the JDK. – David Phillips Dec 29 '18 at 3:50

Again the file(1) utility and libmagic(3), on which it is based, can be your friend:

$ file Gwan.class
Gwan.class: compiled Java class data, version 50.0 (Java 1.6)
  • What if you're on Windows? – avgvstvs Apr 18 '14 at 13:55
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    @avgvstvs: then you can still resort to something like Cygwin. Honestly, if you limit your own toolset by restricting your RCE efforts to a single host OS, that's your own fault. Simply put: know what tools to use when and don't be picky based on arbitrary and artificial limitations. – 0xC0000022L Apr 27 '14 at 18:24
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    Cygwin introduces an unnecessary dependency. If you're reversing .class files, on *every JVM you're going to have access to javap. I don't disagree with the rest of what you're saying, but I'm lazy and if I don't have to start a vm or d/l cygwin I'm happier. – avgvstvs Apr 27 '14 at 19:52

You're looking for this on the command line (for a class called MyClass):

On Unix/Linux:

javap -verbose MyClass | grep "major"

On Windows:

javap -verbose MyClass | findstr "major"

You want the major version from the results. Here are some example values:

  • Java 1.2 uses major version 46
  • Java 1.3 uses major version 47
  • Java 1.4 uses major version 48
  • Java 5 uses major version 49
  • Java 6 uses major version 50
  • Java 7 uses major version 51
  • Java 8 uses major version 52

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