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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?
597
In Java, we can use javap -verbose className to print out the Java class file information; the output includes the major version number. Or we can use the javap -verbose JavaClassName | grep major to display only the major version of the Java class file.
Java 8 uses major version 52.
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 2Djavac -target 1.2==>CA FE BA BE 00 00 00 2Ejavac -target 1.3==>CA FE BA BE 00 00 00 2Fjavac -target 1.4==>CA FE BA BE 00 00 00 30Perhaps 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
101
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
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