Visual Basic
You can't use a space, period (.), exclamation mark (!), or the characters @, &, $, # in the name.
You must use a letter as the first character.
You can’t use any names that are the same as the functions, statements, and methods.
The name can't exceed 255 characters in length.
You can’t repeat names within the same level of scope.
Python
There are some reserved words which you cannot use
Other characters can be letters, numbers or _
Case Sensitive
Must begin with a letter (a - z, A - B) or underscore (_)
Can be any (reasonable) length
Java
Cannot begin with a number
Must begin with a letter (a - z, A - B) or underscore (_)
Can be any (reasonable) length
Uppercase characters are distinct from lowercase characters.
Similarities & Differences
Similarities in the languages are that their variables should be made up of Alphanumeric characters. Another similarity is they should refrain from using most symbols. A third similarity is each has reserved words that the language uses for its own purposes.
A difference is that they are not all case sensitive. Another difference is not all of them use the same reserved words for functions and methods. A third difference is Java and Python are platform independent while visual basic is not.