Determine Java class file version

Although latest version of JDK is already JDK 1.6, many servers in production might be still running with JRE 1.4. It is irritating to get error when running a Java program that compile with newer version of JDK.

So it will be good if there is a way to check the Java class file is compiled into which version.

And this is not difficult. The command is as below (if the class file you want to inspect is MyClass.class):

javap -verbose MyClass

And below is the example output:

Compiled from "MyClass.java"
public class MyClass extends java.lang.Object
SourceFile: "MyClass.java"
minor version: 0
major version: 50
Constant pool:
const #1 = class #2; // MyClass
const #2 = Asciz MyClass;
const #3 = class #4; // java/lang/Object
const #4 = Asciz java/lang/Object;
.
.

Below is the details of JDK version (source: Check the class version):

major  minor Java platform version 
45       3           1.0
45       3           1.1
46       0           1.2
47       0           1.3
48       0           1.4
49       0           1.5
50       0           1.6

Update 3 Oct 2014:

J2SE 8 = 52 (0x34 hex),
J2SE 7 = 51 (0x33 hex),

source: http://en.wikipedia.org/wiki/Java_class_file#General_layout