Interesting problem with byte

[Ashish Chopra]

Hi

Following code explains my problem.

       byte a;
       //initialise a to any value
       a *= -1; //no error
       a = a* -1 //compilation error: Cant convert byte to int
       a= -a //compilation error :Cant convert byte to int

Isnt the 1st stmt same as the 2nd/3rd stmt? If not, why?

Thanx in advance...
Ashish

[Arto Pastinen]

Hi!

I haven't check this from specs, but i think that -1 is assumed to be int, so what compiler real tries to do, is following:

a *= (int) -1;

try this: a *= (byte) -1;

- artsi

[Sathya Narayanan Natarajan]

Hi,
This is one of the advantages of the Compound Assignment Operator +=

When you do any integer arithmetic with byte values, the compiler expects you to put an explicit cast before assigning the result to a byte variable.

For example,
byte a = 3;
a = a + 5; //won't compile,
//needs an explicit cast a = (byte) a + 5;

But when you do the same thing with Compound Assignment operator,We are ensuring the Compiler that the resulting value will definitely fit to a byte variable.
See this,
byte a = 3;
a += 5; //Compiles without any error.

Hope this answers your question.
Thanks,
Sathya.

[Jim Yingst]

Isnt the 1st stmt same as the 2nd/3rd stmt? If not, why?

No. Compound assignment operators (+=, -=, *=, etc.) do more than just perform the operation and assign the result to the variable on the left - they also insert a cast to whatever type the variable on the left has. So

    a *= -11;

is equivalent to

    a = (int) (a * -1);

Similarly,

    a += b;

is equivalent to

    a = (int) (a + b);

(Assuming a and b are ints.)

[Ko Ko Naing]

Originally posted by Ashish Chopra:

       byte a;
       //initialise a to any value
       a *= -1; //no error
       a = a* -1 //compilation error: Cant convert byte to int
       a= -a //compilation error :Cant convert byte to int

Isnt the 1st stmt same as the 2nd/3rd stmt? If not, why?

No, the first statement is not the same as the second and the third, because we cannot terminate a statement without a semicolon( behind it... I don't see semicolons behind those lines, except the first line... So the compilation fails...

[Ashish Chopra]

thanx a lot guys....my doubt stands cleared.

[Nischal Topno]

hi guys,
are we sure we are getting the same error

Cant convert byte to int

because when i compile i get the following error

Test.java:5: possible loss of precision
found   : int
required: byte
                b = b * -1;
                      ^
Test.java:6: possible loss of precision
found   : int
required: byte
                b = -b;

for the following code

public class Test {
public static void main (String[] args) {
byte b;
b *= -1;
b = b * -1;
b = -b;
}
}

nischal

[Ashish Chopra]

i tried out the code that u mentioned.
It still gave me the error saying: cannot convert int to byte.

Though I am using eclipse IDE ...

However my question stands answered.
[ March 22, 2005: Message edited by: Ashish Chopra ]