I saw that Java 1.2 is also known as Java 2. Do "Java 1.x" and "Java x" (for example "Java 1.6" and "Java 6") refer to the same version of Java?
And if yes, why the need for this duality?
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Sun Microsystems had back then a bad habit of going through numerous naming changes for its products, and to use confusing name to start with in the first place.
Originally the term "Java" was being used to describe indiscriminately:
With regard to version numbers, as others pointed out it was partly because of marketing, and partly because they simply felt like Java had done such progress a major version upgrade was better suited (for Java 1.2 / Java 2, and when Java 1.5 / Java 5).
I was also probably a little as well to not mess with their internal numbering used in their tracking and development systems. I tend to think of it as 1.x = language version and X = language and product version. It makes sense, as normal users do not need to worry about minor increments and updates, as they encourage automatic updates, and these shouldn't introduce any changes to the language or the bytecode.
Note also that it gets weirder when you look at minor versions and update numbers. For instance, we had a Java 1.3.1 and later Java 1.4.1 and 1.4.2.
However, there were no 1.x.y ever since, it's always been 1.x.0_UPDATE:
Note also that you will also see updates refered to with either of these naming conventions:
And for extra confusion and to keep up with Sun Microsystems' tradition, Oracle now drops announcements like this.
Note also that not only did they get into the habit of changing the numbering, but also the names of the product offerings. So, Java 2 have J2SE (Java 2 Standard Edition), J2EE (Java 2 Enterprise Edition) and J2ME (Java 2 Mobile Edition). Since the introduction of Java 5, these conventions and acronyms have been dropped (though some have an incredibly long resilience, mostly thanks for dumb recruitment agencies who have no clue what they are talking about) in favor of Java SE, Java EE and Java ME, which are sometimes abbreviated - but shouldn't officially - to JSE, JEE (fairly common) and JME.
Your read this page for more information about the current versioning system used by Sun Microsystems and now Oracle since Java 1.3.1.
(For bonus points, try to lookup the history of NetBeans now to see that it was also renamed a few times).
They're also struggling to decide whether they should back-update existing references or not. For instance, this page about older releases uses the old numbering system for old releases, but the newer product names (Java SE 1.1, 1.2, 1.3 and 1.4 were not released with this naming convention).
Maybe they're just screwing with us for fun. Who knows?
They had fun with naming and numbering there too, of course.
The Java Language Specification used to be released with a book "edition" versioning syste,, following product numbers. So:
So far, so good.
Except the "Java Language Specification" was later only re-edited when language changes were introduced in Java 5 (which kind of make sense, you won't publish new book editions just for fun). As this was the 3rd time they were editing it, they called it (tada!) "Java Langauge Specification, 3rd edition".
But obviously, people then started to wonder why 1.3 and 1.4 didn't have a language spec, or why Java 5 was matched with a 3rd edition of the language spec.
So, Java 7 is now just calling it the "Java Language Specification, Java SE 7 Edition", though we often refer to this one as JLS7 for shorthand and to avoid RSI.
For additional fun, look at Microsoft Windows RT's naming fail, or Apple's naming and numbering madness with iPhones, iPads or even iPods.
The short answer: Marketing.
A longer answer: The short form (e.g. Java 6) is the so-called "product version" and is how Java is marketed to users and in press releases, etc.
The longer form (e.g. Java 1.6.0) is the "developer version". It is used internally, and will also be encountered by Java developers (e.g. The
java.version system property uses the long form).
See these pages for more information:
Because book with title "Learn Shiny New Java 3" will be sold out earlier than book with title "What's new in Java 1.3".
So yes, it is mainly marketing reasons. On the other hand, I don't see a severe crime here. After all, in some products, like Mozilla or Chrome, major build number is constantly get incremented, and others stick to incrementing minor build number, though, sometimes, there are big changes coming up with each new release.
Some, like Apple, don't want to leave us, users, with dull names like "Mac OS 10.6".
And Sun used to be OK with N alias instead of introducing "Java Green Diplodocus" release.
TheServerSide explains change from "Java 1.x" to "Java x" as follows:
Sun has cut off the "1." to change J2SE 1.5.0 to J2SE 5.0. The reason for the change? Sun claims that "this is the most significant upgrade to the Java platform and programming language since its initial release nearly one decade ago", and that this version is worthy.
Apparently there were talks to rename to "J5SE", but there was thought that the J2EE brand means too much to change.
Aren't version numbers fun?
Read the press release: Sun introduces most significant and advanced Java platform release in 5 years
Sun Microsystems, Inc. (Nasdaq: SUNW), the creator
and leading advocate of Java(TM) technology, today introduced Java 2 Platform
Standard Edition (J2SE(TM)) 5.0, the most significant upgrade to the Java
platform and programming language since its initial release nearly one decade
ago. Known as Project Tiger, this updated Java platform offers dramatic ease
of development, new application monitoring and management features, a
dedicated focus on rich client support for the PC desktop and record-breaking
For the sake of completeness note that 1.X version style hasn't been completely dropped.
"Version 1.5.0" Used by Developers
J2SE also keeps the version number 1.5.0 (or 1.5) in some places that are visible only to developers, or where the version number is parsed by programs. As mentioned, 1.5.0 refers to exactly the same platform and products numbered 5.0...
Also note that as pointed in comments term "J2SE" used above has been later changed to "Java SE".