TextArea, character/string replacement with Image

I started to write a chat application in a class, but it was basic. I was looking at improving what it is able to do. One thing I would like to learn is Emoticons. Replacing the inserted text of :-) with the smiley face.

I would make the exchange after the message string is read and is going to be printed to the text window(Byte[] -> image ->Chatwindow. Later I would alter it to be on key press for the sendText.

Any recommendations or material on this?