Why Java String class is declared as final

Question

Can someone help me to understand why String class in Java is declared as final?

Answer 1

String class is made final in Java in order to make the String objects immutable. Making an object immutable helps in two ways:

1. Security: the system can hand out sensitive bits of read-only information without worrying that they will be altered
2. Performance: immutable data is very useful in making things thread-safe.