I saw this list of major version numbers for Java in another post:
| Java | Major version |
|---|---|
| 25 | 69 |
| 24 | 68 |
| 23 | 67 |
| 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?
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.
javap -verbose MyClass?
javacommand as shown in this answer.Official source for major version number:
Java SE 25 Virtual Machine Specification, Section 1.2. The Java Virtual Machine
From Java 10 up to 24 this can be found in
Virtual Machine Specification, Chapter 4. The class File Format (link for Java 24)
The latest published version of the JVM spec can be found here (including some previous versions)
Chapter 4 of JVM (see link above):
For a class file whose major_version is 56 or above, the minor_version must be 0 or 65535.
For a class file whose major_version is between 45 and 55 inclusive, the minor_version may be any value.
...
A class file is said to depend on the preview features of Java SE N (N ≥ 12) if it has a major_version that corresponds to Java SE N (according to Table 4.1-A) and a minor_version of 65535.
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.
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
file /path/to/a.class also returns a major version of a class while java -XshowSettings:properties -version returns local java.class.version(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)
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.
I did that and it worked.
<class> has been compiled by a more recent version of the Java Runtime (class file version XY.Z), this version of the Java Runtime only recognizes class file versions up to AB.C. And note that bumping the JRE/JDK isn't a cure-all, since some dependencies may do things disallowed by current versions of Java (such as illegal reflective access).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)
