Widening rules for shift

[Cathy Song]

Hi All,
What are the widening rules regarding shift operation?

  
    int i = 10;
    long k = 2;      
    i = i >> k; //works just fine. How?

I know byte/short/char will be widened to an int. But if we are shifting an int by a long, wont int be widened to a long?
Thanks.

[Harwinder Bhatia]

Hi Cathy
This is from the JLS:

The type of each of the operands of a shift operator must be a primitive integral type, or a compile-time error occurs. Binary numeric promotion (�5.6.2) is not performed on the operands; rather, unary numeric promotion (�5.6.1) is performed on each operand separately. The type of the shift expression is the promoted type of the left-hand operand.

Cheers
Harwinder

[Vad Fogel]

Hi Cathy, I'd like to add my 2cents to what Harwinder mentioned.
You must've followed one angry thread where somebody upset asked how come this code

byte b=-128;
System.out.println(b>>>3);

produces a negative result. Make sure you've examined what's going on in there because K&B overlooked this scenario. I didn't have a question like that, but who knows...

[Vishy Karl]

Hi Vad,
Your example of
byte b=-128;
System.out.println(b>>>3);
gave me output of
536870896
Why is it coming so ? Should is not be 16 ?? as 128 / 2 raised to 3 is 16 and the sign is changed to positive as operator >>> is used.
Plz. explain ?

[Sunder Ganapathy]

When you write 'System.out.println(b>>>3)' the result is printed as int.
If you store the result in a byte field and then print it, you would get
the negative value .

[Sunder Ganapathy]

While printing it as byte it is accessing the least significant eight bits .

[Vishy Karl]

HI Sunder,
I am still not getting your point.
If i try to store the result of b>>>3 in a byte it gives me compiler error saying possible loss of precision . Even on casting it gives me the same error.
Can u explain with example ?
Thanks,

[Sunder Ganapathy]

I am giving below the code for your benefit .
I 've also given the output as it appears on the console .
class page172{
public static void main(String[] args)
{

byte b = -128;
byte c=(byte)(b>>>3);
System.out.println(c);
System.out.println(b>>>3);
}
}
/**
-16
536870896
*/

[Vishy Karl]

Thanks a lot for the help,
Bye , thanks again.

[Vad Fogel]

I apologize, what I really meant in the first place was

byte b=-128;
System.out.println(b>>>=3);

And right, when you apply a shift operator, the left operand is promoted to the type of the shift expression, and the result is at least int or wider, so b>>>3 is not tricky.