Guava

Multisets

• Type of collection

Collection behaviour

• Can it have duplicates?
• Is ordering significant? (for equals())
• Iteration order
  • insertion-ordered? (Linked list) comparator-ordered? (Tree) user-ordered? (Array)
  • something else well-defined?
  • or it just doesn't matter?

In general, the first two determine the interface type, and the third tends to influce your choice of implementation

List vs. Set

• Set: unordered equality, no dups
• List: ordered equauality, can have dups

Diagram (31:50)

                 Ordered?
             Y             N
Dups? +--------------+----------+
  Y   |     List     | Multiset |
      +--------------+----------+
  N   | (UniqueList) |    Set   |
      +--------------+----------+

Multiset: unordered equality, can have dups