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= E2is equivalent toE1 = (T) ((E1) op (E2)), whereTis the type ofE1, except thatE1is 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.
*=1.5 an integer otherwise.The compiler does not complain because, according to JLS §15.26.2. Compound Assignment Operators:
A compound assignment expression of the form
E1 op= E2is equivalent toE1 = (T) ((E1) op (E2)), whereTis the type ofE1, except thatE1is evaluated only once.
Thus,
i += lng;
is equivalent to
i = (int)(i + lng);
