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

Determining the JDK Version Used to Compile a .class File

When debugging a "Bad version number in .class file" error in Java, it can be helpful to check the version of the .class files involved. Here's how to obtain this information:

Unix/Linux Environment:

Execute the following command:

javap -verbose MyClass | grep "major"

Windows Environment:

Run this command:

javap -verbose MyClass | findstr "major"

Interpreting the Output:

The output of these commands will include a line that contains "major": followed by a numerical value. This value represents the major version of Java used to compile the .class file:

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

This information can help you determine the version mismatch between the JRE and JDK and adjust your compilation settings accordingly.

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