Question

In Java, I really wonder is there a difference between using a += b; or a = a + b; . Which one should I use principally? I know that first one is something like shortcut but does the compiler get those two indications differently?

Answer 1

See the Java language specification, 15.26.2 Compound assignment operators

To quote the relevant parts:

A compound assignment expression of the form E1 op= E2 is equivalent
to E1 = (T)((E1) op (E2)), where T is the type of E1, except that E1
is evaluated only once.

short x = 3;
x += 4.6;

and results in x having the value 7 because it is equivalent to:

short x = 3;
x = (short)(x + 4.6);

So it is more than syntactic sugar, as

int x = 1;
long a = 2l;
x+= a;

compiles, where

int x =1;
long a =2l;
x = x+a;

gives you a compile error, as was discussed here on StackOverflow quite recently