I suspect you wanted to know which branch of mathematics is most applicible. I'd have to go with discrete math, which includes graph theory, discrete optimization, information theory, game theory, complexity theory, etc. The algorithms course every CS major takes is based on discrete math.
Originally posted by Simon Lee:
I think the Object class.
I've been asked this in an interview (was Reuters BTW) & think it's a great question;
"Name all methods of the Object class"
"Describe what each of the methods do"
"Descibe how you would use/override the methods"
Anybody who calls themselves a Java programmer yet cannot do the above is a fraud.