Possible Duplicate:
Java += operator
In Java, this is not valid (doesn't compile), as expected:
long lng = 0xffffffffffffL; int i; i = 5 + lng; //"error: possible loss of magnitude"
But this is perfectly fine (?!)
long lng = 0xffffffffffffL; int i = 5; i += lng; //compiles just fine
This is obviously a narrowing operation, that can possibly exceed the int
range. So why doesn't the compiler complain?
This is defined in the JLS #15.26.2:
A compound assignment expression of the form
E1 op= E2
is equivalent toE1 = (T) ((E1) op (E2))
, whereT
is the type ofE1
, except thatE1
is evaluated only once.
In other words, i += lng
performs a cast implicitly.
i += lng;
compound assignment operator cast's implicitly.
i+=lng; is same as i = int(i+lng);
FROM JLS:
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.
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