Question

Are a += 10 and a = a + 10 both the same, or is there some difference between them? I got this question while studying assignments in Java.

Answer 1

As you’ve now mentioned casting… there is a difference in this case:

byte a = 5;
a += 10; // Valid
a = a + 10; // Invalid, as the expression "a + 10" is of type int

From the Java Language Specification section 15.26.2:

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.

Interestingly, the example they give in the spec:

short x = 3;
x += 4.6;

is valid in Java, but not in C#… basically in C# the compiler performs special-casing of += and -= to ensure that the expression is either of the target type or is a literal within the target type’s range.