What mechanisms or features ensure the immutability of a string in a programming language?

In Java, strings are immutable due to the following mechanisms:

• The String class is declared as final, which prevents inheritance and modification of behavior.
• The internal representation of a string is a character array (char[]), which is declared as final and is not directly accessible for modification.
• Methods of the String class do not modify the existing object but return a new one when changes are made.

This ensures string safety in a multithreaded environment and allows strings to be used as keys in collections without the risk of modification.