•The same value may appear
more than once in a collection (array, ArrayList or
Map)
–my wife and I have the same
phone number
–“field” and “instance variable”
have the same definition
–in an array, foo[3] may ==
foo[7]
•In a Map, keys are unique
(like index in an array)
•If you want to arrange for one
person to have more than one phone number or one word to
have more than one definition you need to work harder …