difference +=

[Suhita Reddy]

Hi all,


wht is the difference b/w the 2 statements?


a=a+b;
a+=b;



Regards
Suhita

[Ernest Friedman-Hill]

They both do effectively the same thing, although depending on the data types of "a" and "b", there are cases where the second one will compile and the first will not. They both add a and b, and set a to the result.

[Suhita Reddy]

hi,


i m unable 2 understand u r answer.can u see the following pgm and explain me.




public class Test {

static int a;

int b;

public Test() {
int c = ++a + ++a;
b += c++;
}

public static void main(String[] args) {
System.out.print(new Test().b);
}
}

Thanks in advance


Regards
suhita

[Ernest Friedman-Hill]

Aaaaagh, my eyes! Note that anyone who writes code like this in the real world is in big trouble; you find this sort of silliness in SCJP mock questions, and nowhere else.

That said...

int c = ++a + ++a;[b]
This means c is (++a) + (++a). a starts at zero. The first expression in parentheses equals 1, and the second equals 2, so c becomes 3.

[b]b += c++;
b also starts at zero. We add to it the result of evaluating (c++), which is just the value of c. Here, the "++" happens after the value of c is read. So since c is 3, b also becomes 3.

And that's the output.

[James Chegwidden]

OR

by default integers are zero, So

int c = 0;
int b = 0;

c = (1) 1 + (2) 2 = 3

b = b + (c++) = 0 + 3 (4) = 3

So b = 3 and c = 3 just like Ernest said.

JC

[Suhita Reddy]

hi,


i satisfied with u r answer.but why they gave b+=c++ instead of b=c++.b=c++ and b+=c++ both r same.i m in little bit confusion?


Suhita

[Edwin Dalorzo]

All that been said the only differente between a=a+b and a+=b is that += autocasts the result.

int a = 10;
byte b = 0;

b += a; //this compiles fine
b = b + a; //this is a compile time error due to numeric promotion

Hence, when you are using += *= -= or /= operators be careful with precision loss. It is bug hard to find, and your compiler will not even complaint about it.

Regards,
Edwin Dalorzo
[ July 07, 2006: Message edited by: Edwin Dalorzo ]

[Suhita Reddy]

Hi all,

Thanks 2 all who gave reponses.Now i understood clearly.



Regards
Suhita

[Ernest Friedman-Hill]

Originally posted by Suhita Reddy:
hi,r.but why they gave b+=c++ instead of b=c++.?

As I said, this is nothing like real code; the whole point of this code is just to be confusing and hard to read.