Java Major and Minor Versions

Java compiler
major version: 47
classes compiled by jdk 1.3

major version: 48
classes compiled by jdk 1.4

major version: 49
classes compiled by jdk 1.5

Compiled by Ant javac

major version: 47
target= 1.3

major version: 48
target = 1.4

major version: 49
target = 1.5

classes compiled by a newer version of jdk can not be run by an older version of jvm without specifically specifying the targeted source version.