why (String args[]) ??

why does argument of main method contains data type of args array as string and why not integer or float or double?

Because the command line environment (from where applications are started) only understands characters, and has no notion of numbers. Plus, strings can be converted into numbers if need be, but not vice versa.

Main Method is the communication medium between jvm and user, so it should receive the input from user in user understandable format ie String...

I'm sorry, but that doesn't make sense - a number is just as understandable by a user as a string.

My view is as long the number is not associated with some thing it does not have any meaning, 15 can represent a day in a month or money or age, etc etc. it can be a symbol as well. but words are self explanatory (when they are meaningful).