530

I saw this list of major version numbers for Java in another post:

Java Major version
20 64
19 63
18 62
17 61
16 60
15 59
14 58
13 57
12 56
11 55
10 54
9 53
8 52
7 51
6 50
5 49
1.4 48
1.3 47
1.2 46
1.1 45
1.0.2 45

Where does this list come from? Is there a specific reference for this? Preferably something that shows minor versions too?

dan1st
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Robert Mark Bram
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7 Answers7

129

These come from the class version. If you try to load something compiled for java 6 in a java 5 runtime you'll get the error, incompatible class version, got 50, expected 49. Or something like that.

See here in byte offset 7 for more info.

Additional info can also be found here.

Michael
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  • Is there a way to echo the major version number (class version) directly from **javac**, without using an existing class like, `javap -verbose MyClass`? – samus Jun 18 '18 at 16:16
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    No there isn't. – Stephen C Aug 15 '19 at 15:15
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    @samus It's possible from `java`command as shown in [this answer](https://stackoverflow.com/a/75247102/2834978). – LMC Jan 26 '23 at 13:59
46

Official source for major version number:

Java SE 20 Virtual Machine Specification, Chapter 4. The class File Format

The latest published version of the JVM spec can be found here.

dan1st
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29

I found a list of Java class file versions on the Wikipedia page that describes the class file format:

http://en.wikipedia.org/wiki/Java_class_file#General_layout

Under byte offset 6 & 7, the versions are listed with which Java VM they correspond to.

Peter
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10

If you have a class file at build/com/foo/Hello.class, you can check what java version it is compiled at using the command:

javap -v <path to class file> | grep "major"

Example usage:

$ javap -v build/classes/com/example/Book.class | grep major
  
major version: 57

According to the table in the OP, major version 57 means the class file was compiled to JDK 13 bytecode level

Andy Guibert
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4

(Really an extended comment than an answer ..)

The question was regarding "where does the list of versions come from".

That was answered in this response, which references the JAVA SE Specification on: "The class File Format". Seems that's pretty authoritative (it's also referenced in the Wiki for the byte 6 (major version) values) and should be the accepted answer.

Several answers seem to focus on how to determine the value using javap or not using it. Those should be separate questions. Nevertheless, a non- javap means of finding the version is unix command file. file reads the magic, which is specified in the ClassFile structure.

ie: file myClass.class, or more elegantly, file -b myClass.class | awk -F',' '{print $NF}'

eg:

$ find * -name "*.class" -exec file -b {} \; | awk -F',' '{print $NF}' | sort -u
 version 45.3
 version 50.0 (Java 1.6)
 version 52.0 (Java 1.8)
Ian W
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3

If you're having some problem about "error compiler of class file", it's possible to resolve this by changing the project's JRE to its correspondent through Eclipse.

  1. Build path
  2. Configure build path
  3. Change library to correspondent of table that friend shows last.
  4. Create "jar file" and compile and execute.

I did that and it worked.

Das_Geek
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JeffersonSousa
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2

I use javap in my .lessfilter for classes, so I can decompile and know what version they were compiled with directly

*.class)
echo "/** "
javap -verbose "$1" | grep version | sed -e 's/50/Java6/' -e 's/51/Java7/' -e 's/52/Java8/' -e 's/53/Java9/' -e 's/54/Java10/' -e 's/55/Java11/' -e 's/56/Java12/' -e 's/57/Java13/'
echo " **/"
java -jar ~/bin/cfr-0.150.jar "$1" | enscript --color --language=ansi --highlight=java -o - -q
;;

(tried to add as a comment to previous answer, but couldn't get the code to be formatted, and thought this might be useful for others)

Scott Carlson
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