Write the return type of the following library functions: (i) isLetterOrDigit(char) (ii) replace(char, char)

(i) boolean (ii) String

(i) Character.isLetterOrDigit() asks whether a character is a letter or a digit — a yes-or-no question, so boolean. Every is... method of the Character class behaves the same way. (ii) replace() produces a NEW string with every occurrence of one character swapped for another, and returns it as a String. Note that the original string is unchanged, because Strings are immutable — which is why the method must return something rather than modify in place.