The one true place to look is
http://www.unicode.org/.
Text files on disk may sometimes have a few bytes at the start, indicating their Unicode encoding. This is called the Byte Order Mark, or BOM. If it is there, you can determine the encoding with certainty, and hence decode the text file correctly.
Java is pretty good at that stuff: see
String, Reader, Writer etc.
If there is no BOM in a text file, there is no 100% guaranteed way to determine its encoding. Some Third-party frameworks (don't know any URLs - try Google) will try to guess it for you.
Oh, and please don't use this text-messaging abbreviation garbage in your posts. You have a real keyboard, so type "difference between", not "diff b/w". Using unnecessary abbreviations annoys some readers, and also makes it harder for people who have limited English.
[ June 26, 2006: Message edited by: Peter Chase ]