Why does this assignment not require an explicit cast?

Question

Consider this code:

byte b=1;
long l=1000;
b += l;

I would expect the last statement to require an explicit cast because, b+=l is evaluated as b = b+l and (b+l) part gives an integer. Integer cannot be assigned to byte without an explicit cast?

possible duplicate of Java += operator

assylias
– assylias

2012-11-28 11:04:49 +00:00
Commented Nov 28, 2012 at 11:04 — assylias
– assylias, Commented Nov 28, 2012 at 11:04

Jon Skeet · Accepted Answer · 2012-11-28 11:01:31Z

18

Well to start with, b+l gives a long, not an int...

... but compound assignment operators have other behaviour. As per JLS 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.

Note the cast to T.

answered Nov 28, 2012 at 11:01

Jon Skeet

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2 Comments

Fabian Lange Over a year ago

you can observe the difference when you manually write b = b + l; then you will see the error you want :-)

PrashanD Over a year ago

Sorry, b+l gives a long. And I need to read the oracle docs more. Thanks.

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