ASCII is a (by today's standards) old encoding scheme that maps number codes to alphanumeric symbols. There are 127 characters in the basic ASCII character set,including letters, numbers, and punctutation symbols from the Western English alphabet. ASCII isn't very useful in international settings since it's missing a lot of symbols that other languages use.
That's why
java uses Unicode. Unicode is another type of encoding that can define up to 65,535 different characters, and is therefore able to handle most of the characters in every language on the planet.
See also here:
http://www.mindprod.com/gloss.html scroll down and look for ASCII.