Java dropped the leading 1 with version 5 since Sun decided it would never go for a complete rewrite of the language. Imagine the chaos if Python did that and then pulled the 2 to 3 change on a run of the mill update from 213 to 214.
Java 1.2 was branded as "Java 2", so you had the J2SE (Java 2, Standard Edition) and related J2ME and J2EE (Mobile and Enterprise, respectively) platforms. The "Java 2" moniker was dropped in Java 5, which was the largest rewrite of the language since, adding generics, sane memory model, annotations, etc., all in the same language revision.