List vs Queue vs Set of collections in Java

Question

what is the difference among list, queue and set?

Answer 1

In brief:

A list is an ordered list of objects, where the same object may well appear more than once. For example: [1, 7, 1, 3, 1, 1, 1, 5]. It makes sense to talk about the "third element" in a list. You can add an element anywhere in the list, change an element anywhere in the list, or remove an element from any position in the list.

A queue is also ordered, but you'll only ever touch elements at one end. All elements get inserted at the "end" and removed from the "beginning" (or head) of the queue. You can find out how many elements are in the queue, but you can't find out what, say, the "third" element is. You'll see it when you get there.

A set is not ordered and cannot contain duplicates. Any given object either is or isn't in the set. {7, 5, 3, 1} is the exact same set as {1, 7, 1, 3, 1, 1, 1, 5}. You again can't ask for the "third" element or even the "first" element, since they are not in any particular order. You can add or remove elements, and you can find out if a certain element exists (e.g., "is 7 in this set?")