List of Java class file format major version numbers?

Question

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

Java	Major version
22	66
21	65
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?

Trotskyite

Answer 1

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.

Ashy

Is there a way to echo the major version number (class version) directly from javac, without using an existing class like, javap -verbose MyClass? – Pazpaza

No there isn't. – Deadfall

@Pazpaza It's possible from javacommand as shown in this answer. – Whangee

Answer 2

Official source for major version number:

Java SE 21 Virtual Machine Specification, Chapter 4. The class File Format

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

Pulsimeter

Answer 3

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.

Glaydsglaze

Answer 4

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

Denunciatory

file /path/to/a.class also returns a major version of a class while java -XshowSettings:properties -version returns local java.class.version – Schwinn

Answer 5

(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)

Congregationalism

Answer 6

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.

Uracil

Answer 7

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)

Brutus