What changed in Java 2 (1.2)

2 changes across 2 questions — each with the behaviour it replaced, because “and how did it work before?” is the follow-up.

• How does HashMap work internally?

  • HashMap arrives in the collections framework, unsynchronized, permitting one null key and any number of null values.

    Before: Hashtable was the only choice: every method synchronized whether you needed it or not, and it throws NullPointerException on a null key or value.

• When would you use LinkedList instead of ArrayList?

  • ArrayList and LinkedList arrive with the collections framework, unsynchronized so you pay for locking only when you ask for it.

    Before: Vector was the only growable list, and every method was synchronized whether or not the list was shared.