Question

I know that Strings are immutable.

Then, what is the difference between:

String name ="Name";
final String name ="Name";

Why do we use final in this context? Because String is already immutable there seems to be no need. Second related question, why are String’s immutable?. Other Data Types like int, boolean are not. If String is immutable does that make it thread-safe? I read that “if String been mutable, a request to load “java.io.Writer” could have been changed to load “mil.vogoon.DiskErasingWriter”” means ?

Answer 1

There are a lot of questions here, but here are a few notes that should answer most of them:

• final means the variable can be assigned only once. It has nothing to do with mutability, which is a property of the object, rather than the variable (which is simply a handle)
• String is immutable, because you can’t change its internal state (it has a private char[] chars that hold the characters). Primitives are also immutable. This is better visible in their wrapper equivalents – Integer, Long etc.
• yes, a String is thread-safe, because its state cannot be changed no matter how many threads work with it. Every operation on the string results in a new instance, rather than changing the existing one.