is it compulsion to make field as final to make class immutable

Question

I have doubt a doubt regarding making an immutable class.

As per the java docs.

1. I made the class final( no one can extend)
2. field are private.
3. no setter function.
4. If fields are mutable then send a cloned copy of the field.

My doubt is that its compulsory to make a field of my class as final?

Answer 1

If there are no setter methods (and presumably no other methods to affect the fields' values) and the fields themselves are private, marking them as final is somewhat redundant. Having said that - its a good defensive practice which many projects' standards follow.