You can implement your own spellcheck with a dictionary (it can be quite large depending on the supported languages), and then distance metrics are calculated from the words in the text box in the dictionary. Underline can be done by styling the font, there as a sample applet here .
Jaspell is the Java implementation of the popular Aspell. It has some explanations for the search algorithms used.
As mentioned earlier, Jazzy is also great, and IBM provides a good tutorial .
whatnick
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