Why can't strings be mutable in Java and .NET?

Question

Why is it that they decided to make String immutable in Java and .NET (and some other languages)? Why didn\'t they make it mutable?

Answer 1

Immutability is good. See Effective Java. If you had to copy a String every time you passed it around, then that would be a lot of error-prone code. You also have confusion as to which modifications affect which references. In the same way that Integer has to be immutable to behave like int, Strings have to behave as immutable to act like primitives. In C++ passing strings by value does this without explicit mention in the source code.