Simple add method Thread safe?

Question

Having this simple class, with addition method :

class A {
   public Integer add (int a, int b){
     return a+b;
   }
}

is it thread safe or not..? it looks safe for me, but most poeple answer no, could anyone explain why?

Answer 1

Thread safety should be bothered about only when you have some means of sharing state and you modify that without any locks or synchronization i.e. you modify a shared variable(class level variable) then only you should care about thread safety.
Here there is no issue of thread safety.
And in this particular case each variable is local and that location will not be shared by threads as each function call will have their on separate allocation on stack along with their local variables you should not bother anyways :)