In Effective Java (Item 15 [“Minimize Mutability”] in the Second Edition and Item 13 [“Favor Immutability”] in the First Edition), Joshua Bloch extols the virtues of immutable objects and ...

In Immutable Objects in Java, the four authors (Haack, Poll, Schafer, and Schubert) include a section on “enforcing immutability.” ...

Immutable objects are handy since they help with thread-safety and even just semantically since for many objects, if you modify it, it shouldn't be considered the same object.