Are all final class immutable?

Question

Are all final classes in Java immutable. String and Integer both are final classes and both are immutable i beleive.

Answer 1

As has been said by the others before final does not make a class imuutable in Java though it plays a part in the immutability strategy. To obtain immutability you should follow the general guidlines:

• ensure the class cannot be overridden - make the class final, or use static factories and keep constructors private
• make fields private and final
• force callers to construct an object completely in a single step, instead of using a no-argument constructor combined with subsequent calls to setXXX methods (that is, avoid the Java Beans convention)
• do not provide any methods which can change the state of the object in any way - not just setXXX methods, but any method which can change state
• if the class has any mutable object fields, then they must be defensively copied when passed between the class and its caller

Answer 2

No, final means the class can not be extended. It says nothing about mutability. For example:

final class MutInt {
   public int modifyMe;
}