how to check the jdk version used to compile a .class file


Possible Duplicate:
Tool to read and display Java .class versions

I'm trying to debug a

"Bad version number in .class file'

error in java, is there a way for me to check which version the .class files are?

I'm using JRE1.5.0_6, but my JDK is version 1.6.0_13.

I'm compiling with compatibility mode set to 1.5 in eclipse which I thought would work...

5/23/2017 11:54:47 AM

Accepted Answer

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
  • Java 9 uses major version 53
  • Java 10 uses major version 54
  • Java 11 uses major version 55
10/18/2018 2:56:26 PM

Btw, the reason that you're having trouble is that the java compiler recognizes two version flags. There is -source 1.5, which assumes java 1.5 level source code, and -target 1.5, which will emit java 1.5 compatible class files. You'll probably want to use both of these switches, but you definitely need -target 1.5; try double checking that eclipse is doing the right thing.


Free JarCheck tool here


You can try jclasslib:

It's nice that it can associate itself with *.class extension.


Does the -verbose flag to your java command yield any useful info? If not, maybe java -X reveals something specific to your version that might help?


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