Why is String immutable in Java (actual reason not the rattafied one)

Main ones:

1. String pool. Java reuses the same object for identical literals. If strings could change, changing one would change it for everyone using that literal. Immutability is what makes the pool safe.

2. Security. Things like file paths and DB urls are strings. If they were mutable, code could pass a check with one value and then change it after the check.

3. Thread safety, you can share them between threads without locks.

4. hashCode is cached inside String. That only works because the content can never change, and it's why String keys in HashMap are cheap.

If you can explain 1 and 4 with an example you're fine in most interviews.