I don't even know what Java 6 means. Last time I wrote something in Java it said Java 1.5
compiled Java class data, version 49.0 (Java 1.5) compiled Java class data, version 49.0 (Java 1.5)They started with Java 1.0 and 1.1 - then to "Java 2" at version 1.2, so you have Java 2 version 1.2 ... they then stuck with that through the version after 1.4 - but rather than 1.5, that was special as it was Java 2 version 5.0 ... thereafter they're just numbered with the plain number.
$ java -version
java version "1.8.0_391"
Java(TM) SE Runtime Environment (build 1.8.0_391-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.391-b13, mixed mode)
For the JRE, I want to say that they stuck with the 1.version.minor numbering (although the last version with a minor other zero was I think the Very Popular And Probably Still In Prod 1.4.2), with updates suffixed with "u" + number through the Java 8 series, but then with 9 they switched to version.minor.update instead.
It's completely incomprehensible; not even Oracle can keep it straight.