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

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...

See http://stackoverflow.com/questions/698129/how-can-i-find-the-target-java-version-for-a-compiled-class — Jonathan Holloway, Jul 08 '09 at 04:58
Check out [javadoc](http://java.sun.com/docs/books/jvms/second_edition/html/ClassFile.doc.html) for more information on major and minor versions. — WiseGeek, Jul 08 '09 at 05:33

score 726 · Accepted Answer · edited Jun 07 '23 at 19:53

726

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

edited Jun 07 '23 at 19:53

Nicolas Filotto

43,537
11
94
122

answered Jul 08 '09 at 04:53

John Calsbeek

35,947
7
94
101

57

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: http://en.wikipedia.org/wiki/Java_class_file#General_layout – Jim Apr 24 '14 at 11:19
23

addendum: You can put -cp then the class so you can get it from and existing jar – Christian Bongiorno Dec 04 '14 at 17:32
3

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. http://stackoverflow.com/questions/13356811/java-javap-errorcould-not-find-class – Kyle Bridenstine Dec 01 '15 at 19:21
2

As Jim advises, for vi addicts: "vi MyClass" then " :!xxd" then peep at byte 8; 0x31, 0x32, 0x33, 0x34, 0x35 stands for java 5, 6, 7, 8, 9 respectively. " :q!" to exit vi. – user3526918 Sep 09 '17 at 14:28
1

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? – Paramvir Singh Karwal Nov 20 '18 at 13:32
So, this major version is in sequence? so for next Java 12 coming march will be 56 ? – DAIRAV Nov 27 '18 at 07:29
1

The manifest Build-Jdk seems to be the JDK that made the jar file, which could be different from the JDK of the compiler. – Bruce Sep 22 '19 at 09:09
[From inside your program](https://stackoverflow.com/questions/27065/tool-to-read-and-display-java-class-versions/58642950#58642950) – Marinos An Oct 31 '19 at 12:13
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" – Fahim Aslam Bhatti Nov 07 '19 at 13:12
Could anybody add the major versions for Java >= 12? – Matthias Boehm Feb 07 '22 at 15:17
what about an aar? – Fran Marzoa May 30 '22 at 14:20

score 17 · Answer 2 · answered Jul 08 '09 at 05:39

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.

score 9 · Answer 3 · answered Jul 18 '09 at 12:01

9

Free JarCheck tool here

answered Jul 18 '09 at 12:01

Gwyn Evans

1,361
7
17

score 6 · Answer 4 · edited Jun 04 '14 at 12:53

6

You can try jclasslib:

https://github.com/ingokegel/jclasslib

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

edited Jun 04 '14 at 12:53

Vadzim

24,954
11
143
151

answered Aug 02 '11 at 07:37

marekdef

481
4
10

score 3 · Answer 5 · answered Jul 08 '09 at 04:55

3

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?

answered Jul 08 '09 at 04:55

Alex Martelli

854,459
170
1,222
1,395

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

5 Answers5

Linked

Related

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

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

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