The problem in java is that one has to live with all those objects, where the class looks like:
class Mutable {
State1 f1;
MoreState f2;
void doSomething() { // mutate the state, but don't document it }
void doSomethingElse() /// mutate the state heavily, do not mention in doc
}
(Note the missing Cloneable interface).
The problem with the garbage collector is not such a big one nowadays. The VM's are happy with short living objects.
Advances in Compiler/JIT technology will make it possible, sooner or later, to optimize intermediate temporary object creation away. For example:
BigInteger three =, two =, i1 = ...;
BigInteger i2 = i1.mul(three).div(two);
The JIT could notice that the intermediate object i1.mul(three) can be used for the end result and call a variant of the div method that works on a mutable accumulator.
