How to Determine the JDK Version Used to Compile a .class File?

How to Check the JDK Version Used to Compile a .class File

Checking the Version

When encountering the error, "Bad version number in .class file," it can be helpful to determine the version of the .class files in question. Here's a cross-platform approach to checking the major JDK version used to compile a .class file:

Unix/Linux

javap -verbose MyClass | grep "major"

Windows

javap -verbose MyClass | findstr "major"

Interpreting the Output

The output of the above command will include a line similar to:

major version: 50

This value corresponds to the major JDK version used to compile the .class file. Refer to the table below for a mapping between major version numbers and Java versions:

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

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