Given a class file, which JDK was used?

Hello.

Given a class file, is there a quick way to know which JDK should be used to run it?

Basically I would like to know if it's compiled for JDK 5 or also support 1.4

Cheers,

Renato

Have a look at the Java Virtual Machine Specification, Class File Format. The major and minor version are what you are looking for.

A quick way to get this info is with the javap tool (which comes with the JDK):

javap -verbose MyClass

gives you something like:

The major and minor version are what you want. These are described in the link Joe gave, specifically in footnote 1 - except unfortunately that only covers up through JDK 1.2, the most current release aat the time the JVM spec 2nd edition came out. The most current info is accessible through "Maintenance Infoormation", which eventually leads here. Footnote 1 now reads:

"1 The Java virtual machine implementation of Sun�s JDK release 1.0.2 supports
class file format versions 45.0 through 45.3 inclusive. Sun�s JDK releases 1.1.X can support class file formats of versions in the range 45.0 through 45.65535 inclusive. For k ? 2 implementations of version 1.k of the Java 2 platform can support class file formats of versions in the range 45.0 through 44+k.0 inclusive. "

Which means:

JDK 1.2 uses major version 46
JDK 1.3 uses major version 47
JDK 1.4 uses major version 48
JDK 1.5 uses major version 49
JDK 1.6 uses major version 50

Hi guys, thanks for the info! Very useful indeed.

Thanks again.

Renato

javap ? This is cool. Except that when I tried it on file compiled with 1.4, I have :
Compiled from "DoubleComboJSON.java"
public class ajax.DoubleComboJSON extends javax.servlet.http.HttpServlet
SourceFile: "DoubleComboJSON.java"
minor version: 0
major version: 0
Constant pool:
...

Look at the 5th, 6th, 7th and 8th byte in the class file to derive the major and minor version number.