Both version numbers (1.6.0 and 6) are used to identify the release of the Java Platform. Version 6 is the product version, while 1.6.0 is the developer version. The number 6 is used to reflect the evolving level of maturity, stability, scalability and security of Java SE.
Java SE keeps the version number 1.6.0 (or 1.6) in some places that are visible only to developers, or where the version number is parsed by programs. As mentioned, 1.6.0 refers to exactly the same platform and products numbered 6. Version numbers 1.6.0 and 1.6 are used at:
* java -version (among other info, returns java version "1.6.0")
* java -fullversion (returns java full version "1.6.0-bxx")
* javac -source 1.6 (is an alias for javac -source 6)
* java.version system property
* java.vm.version system property
* @since 1.6 tag values
* jdk1.6.0 installation directory
* jre1.6.0 installation directory
*
http://java.sun.com/javase/6 website (
http://java.sun.com/javase/1.6.0 also works)