Fun with javap

I finally was able to try out javap for the first time today. I needed to know what version of Java a class file was compiled in and javap came to the rescue! To determine the version simply run javap on the class.

javap -verbose my/compiled/class

This will dump a bunch of information about your class file. The only thing you are looking for is the major version up at the top. It should look something like this.

$ javap -verbose aTest/service/EJBHelloService
Compiled from "EJBHelloService.java"
public class aTest.service.EJBHelloService extends javax.xml.ws.Service
 SourceFile: "EJBHelloService.java"
 RuntimeVisibleAnnotations: length = 0x15
  00 01 00 24 00 03 00 1C 73 00 25 00 26 73 00 27
  00 28 73 00 29
 minor version: 0
 major version: 50
 Constant pool:
const #1 = Method       #16.#42;        //  javax/xml/ws/Service."":(Ljava/net/URL;Ljavax/xml/namespace/QName;)V
const #2 = Field        #15.#43;        //  aTest/service/EJBHelloService.EJBHELLOSERVICE_WSDL_LOCATION:Ljava/net/URL;
const #3 = class        #44;    //  javax/xml/namespace/QName
const #4 = String       #39;    //  http://service.aTest/
...

The versions of Java go like this:

Java 6 50
Java 5 49
Java 1.4.2 48
Java 1.3.1 47
etc ...