How can I find the target Java version for a compiled class?

Question

Duplicate:

Tool to read and display Java .class versions

If I have a compiled Java class, is there a way to tell from just the class file what its target version compatibility is? Specifically, I have a number of class files, compiled to Java 6, which are running under Java 5 and giving the the "Unrecognized version" error. I want to be able to look at a class file and find what its target version compatibility is without running the JVM. Any ideas?

... and of course, the file utility is also included on MacOS, if you're willing to use the Terminal. — kmorris, Jul 25 '13 at 02:46

score 45 · Answer 1 · answered Mar 30 '09 at 17:22

45

You can use the javap utility that comes with the standard JDK.

javap -verbose MyClass

Compiled from “MyClass.java”
public class MyClass extends java.lang.Object
SourceFile: “MyClass.java”
minor version: 3
major version: 45

answered Mar 30 '09 at 17:22

bruno conde

47,767
15
98
117

while it may be considered "better" it is not exactly what I was looking for. – Mike Pone Mar 30 '09 at 17:47
4

Same result can be achieved using file program (on most GNU/unix system) : file Foo.class Foo.class: compiled Java class data, version 45.3 BTW: how to compile to produce this output (45.3) , is .45 jdk1.x or j2me ? – RzR Apr 01 '11 at 08:44
6

There is a table of major version numbers (like major version 51 = Java 1.7 and so on), on the [Wikipedia article for Java class file](http://en.wikipedia.org/wiki/Java_class_file#General_layout). – rescdsk Jan 05 '12 at 17:49
1

The exact version can be dumped using "javap -version target.class" – user2149140 Mar 28 '18 at 21:45
1

@user2149140 `javap -version` reports the version of `javap`, not your `target.class` – Cardin Aug 14 '20 at 05:58

score 25 · Accepted Answer · edited Mar 30 '09 at 17:24

25

I've found this on the net and it works.

Every '.class' file starts off with the following:

Magic Number [4 bytes]

Version Information [4 bytes]

A hexdump of a '.class' file compiled with each of the following options reveals:

javac -target 1.1 ==> CA FE BA BE 00 03 00 2D
javac -target 1.2 ==> CA FE BA BE 00 00 00 2E
javac -target 1.3 ==> CA FE BA BE 00 00 00 2F
javac -target 1.4 ==> CA FE BA BE 00 00 00 30

Perhaps you could use this information to write your own '.class' file version checking utility, using Java, or perhaps a scripting or shell language ;) !

I hope this helps.

Anthony Borla

From: http://bytes.com/groups/java/16603-how-determine-java-bytecode-version

edited Mar 30 '09 at 17:24

Michael Myers

188,989
46
291
292

answered Mar 30 '09 at 17:19

Kalecser

1,143
12
15

Great, but what about versions 1.5 and 1.6, which are the ones I care about? – Mike Pone Mar 30 '09 at 17:29
1

Seems like the last number represents the final version hex 31 = dec 49 hex 32 = dec 50. That's what I need. Thanks. – Mike Pone Mar 30 '09 at 17:32
3

Version 1.6 = 32 and 1.5 is 31 – Kalecser Mar 30 '09 at 17:35
2

I found the answer [provided here](http://stackoverflow.com/questions/1096148) to be slightly more enlightening. – Scott Nov 15 '14 at 19:05
5

`javap -verbose MyClass` => Major Version 49 (decimal)= Java 1.5, 50= Java 1.6, 51= Java 1.7, 52= Java 1.8. – FoggyDay Dec 17 '14 at 22:21

score 5 · Answer 3 · answered Apr 25 '13 at 14:42

Linux/Unix users have a nice tool out of the standard toolbox: file utility. Modern versions can detect the Java class fersion version and even output Java version for known class file types.

Example output:

com/sample/Tracker.class: compiled Java class data, version 45.3
com/sample/TestListener.class: compiled Java class data, version 49.0 (Java 1.5)

And it fits very nicely into the standard Unix scripting toolchain.

score 3 · Answer 4 · edited Sep 09 '15 at 18:08

Taken from: http://twit88.com/blog/2008/09/22/java-check-class-version/

try {
    String filename = "C:\\MyClass.class";
    DataInputStream in = new DataInputStream(new FileInputStream(filename));
    int magic = in.readInt();
    if (magic != 0xcafebabe) {
        log.info(filename + " is not a valid class!");
    }
    int minor = in.readUnsignedShort();
    int major = in.readUnsignedShort();
    log.info(filename + ": " + major + " . " + minor);
    in.close();
} catch (IOException e) {
    log.info("Exception: " + e.getMessage(), e);
}

score 0 · Answer 5 · answered Mar 30 '09 at 17:19

0

You can look at the byte offset 6 and 7 in the file (in a hex dump probably), which tells you which version is used. I think the Bytecode Visualizer (eclipse plugin) can see which version a class file is made for.

How can I find the target Java version for a compiled class?

Duplicate:

5 Answers5

Linked

Related