As we all know, String is immutable in java. however, one can change it using reflection, by getting the Field and setting access level. (I know it is unadvised, I am not planning to do so, this question is pure theoretical).
my question: assuming I know what I am doing (and modify all fields as needed), will the program run properly? or does the jvm makes some optimizations that rely on String being immutable? will I suffer performance loss? if so, what assumption does it make? what will go wrong in the program
p.s. String is just an example, I am interested actually in a general answer, in addition to the example.
You are definitely asking for trouble if you do this. Does that mean you will definitely see bugs right away? No. You might get away with it in a lot of cases, depending on what you're doing.
Here are a couple of cases where it would bite you:
functionand somewhere it is being called like
function("Bob"); in this scenario the string
"Bob"is changed throughout your app (this will also be true of string constants declared as
I know this question is about Java, but I wrote a blog post a while back illustrating just how insane your program may behave if you mutate a string in .NET. The situations are really quite similar.