Why are Java wrapper classes immutable?

Question

I know the usual reasons that apply to general immutable classes, viz

1. can not change as a side effect
2. easy to reason about their state
3. inhe

Answer 1

There are mutable, thread safe wrappers as well for some types.

AtomicBoolean
AtomicInteger
AtomicIntegerArray
AtomicLong
AtomicLongArray
AtomicReference - can wrap a String.
AtomicReferenceArray

Plus some exotic wrappers

AtomicMarkableReference - A reference and boolean
AtomicStampedReference - A reference and int