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

Question

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...

Spinning

See #698629 – Insessorial

Check out javadoc for more information on major and minor versions. – Lalalalage

Answer 1

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 Version	Major Version
1.2	46
1.3	47
1.4	48
5	49
6	50
7	51
8	52
9	53
10	54
11	55
12	56
13	57
14	58
15	59
16	60
17	61
18	62
19	63
20	64
21	65
22	66

Taxicab

Alternatively, if you open the class file in a hex editor you can look at bytes 7 and 8. The number will map to the numbers given in the above answer. E.g. 00 2E -> JDK 1.2 = 46 (0x2E hex). Useful if you don't have access to javap. ref: en.wikipedia.org/wiki/Java_class_file#General_layout – Platonism

addendum: You can put -cp <jar> then the class so you can get it from and existing jar – Mckibben

I had to remove the ".class" in the command otherwise I got a message, "Error: Cannot find foo.class". So doing, "javap -verbose foo | grep "major"" worked. Just a heads up. #13357311 – Dorita

As Jim advises, for vi addicts: "vi MyClass" then "<Esc> :!xxd" then peep at byte 8; 0x31, 0x32, 0x33, 0x34, 0x35 stands for java 5, 6, 7, 8, 9 respectively. "<Esc> :q!" to exit vi. – Roseanneroseate

So I was working on a project that uses amazon sdk. The project uses Java 1.7. If I check inside of the MANIFEST.MF of amazon sdk it says Build-Jdk: 1.8.0_111 , but if I use javap -verbose MyClass | grep "major" it says major version: 50 which means Java Version 6. This is confusing. Does that mean - even though it was compiled with 8 but it can run on 6? – Heavyladen

So, this major version is in sequence? so for next Java 12 coming march will be 56 ? – Belen

The manifest Build-Jdk seems to be the JDK that made the jar file, which could be different from the JDK of the compiler. – Wheatear

From inside your program – Slack

Just for information, On Windows we can use following command to find major version of jdk with which the class was compiled: javap -verbose Xyz.class | findstr "major" – Dominate

Could anybody add the major versions for Java >= 12? – Smith

what about an aar? – Cluny

Answer 2

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.

Masquerade

Answer 3

Free JarCheck tool here

Suk

Answer 4

You can try jclasslib:

https://github.com/ingokegel/jclasslib

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

Iseabal

Answer 5

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?

Sadness