Why const keyword is not used in Java?
Actually, the Wikipedia article you linked has your answer:
An enhancement request ticket for implementing const correctness exists in the Java Community Process, but was closed in 2005 on the basis that it was impossible to implement in a backwards-compatible fashion.
It is not used because it has no function in Java. I quote from Wikipedia:
Although reserved as a keyword in Java, const is not used and has no function.
Therefore you should use final instead.
Here is another, maybe more reliable source.
Can you see reasons for closing the request, does Sun provides any explanations?
Yes. Sun provided 3 reasons for why they won't act on the request in the request itself. I quote:
"There are no current plans to add this feature to Java. In addition to creeping featurism, we see the following problems with this feature:
Adding const is too late now. Had this been added from 1.0, the situation could have been different.
Const pollution: the C++ approach requires all const methods to be marked with a const keyword. This means that most methods will have to be marked const explicitly. This tend to clutter all methods in C++.
Compatibility is a very important feature of the JDK. Arguably, the collection classes should be modified to indicate that the elements are const. That would require all existing implementations to be updated in the same way, effectively breaking all existing non-JDK implementations of the collection interfaces. Similarly, hashCode would have to be const, breaking the current implementation of String."
UPDATE
Out of curiousity, I spent a few minutes trawling through the subject lines of the Project COIN mailing list. Somewhat to my surprise, nobody bothered to suggest const. (Or if they did, I missed it.)
So either nobody cares (enough) for this idea any more, or people with sufficient expertise to formulate a project COIN proposal recognize that there's no chance that it would pass muster.