Java invariance, using the “=” operator

The questions about string invariance in java have plenty, in which the author of the problem actually reassigns references

However, there is a significant case where there seems to be no reallocation of strings:

String s = "hello";
s += " world";

You think of it as an actual modification of the string Try it at home

I'm sure it's a syntax sugar and translated by the compiler into something with the same semantics:

String s = "hello";
s = s + " world";

Can anyone confirm this fact?

Solution

I can neither confirm nor deny it If the optimization compiler can prove to itself that no other thread can "see" the initial (pre - =) value of S, it is free to optimize the concatenation and compile the code into an equivalent

String s = "hello world";

As long as the compiler follows the memory model, the compiler is free to convert them from source code to byte code