How the final keyword work with StringBuilder?

Question

Why below code is not throwing any exception while final used?
final StingBuilder sb=new StingBuilder("Satya");
sb.append("Pune");

Answer 1

final only says the variable cannot be reassigned. but the attributes of the variable can still be changed

final means in this case: that the reference to the object is final (it can only be assigned once), not the object itself.

The object itself can still be modified.

Answer 2

final means shallow immutability.

Java only has primitive and reference variables and in this case StringBuilder sb is a reference to a StringBuilder and that reference is immutable. ie. you can't do sb = null; later.

However, the object referenced is not made also immutable and you can still call methods which alter the StringBuilder via this reference.