Unexpected output in Java while adding of two Integers

Question

I am new in java language, here is m not able to understand, why program returning -2 after adding two full range integers.

class Variables {
    public static void main(String[] args) {
        int a = 2147483647;
        int b = 2147483647;
        long c = a + b;
        System.out.println( c );
    }
}

I am expacting 4294967294 value in my variable c, but why it returns -2 please explain me the reason behind this

You just reach Integer Overflow, the int are first summed as ints, then cast to long, but too late — azro, Mar 21 '20 at 18:14
Suggestion - learn how integers are represented in memory / binary. Then learn binary addition. Then you'll understand better — OneCricketeer, Mar 21 '20 at 18:17

score 0 · Answer 1 · answered Mar 21 '20 at 18:16

0

The result of adding two ints is an int, which of course overflows when you add a and b. Only then is it promoted to a long.

You can get the result you expected by casting one of them to long before performing the addition:

long c = ((long) a) + b;

answered Mar 21 '20 at 18:16

Mureinik

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score 0 · Accepted Answer · answered Mar 21 '20 at 18:16

You reach Integer.MAX_VALUE so you're going to -2147483648, then adding Integer.MAX_VALUE again will result in -2

To get 4294967294, you need to cast one value as long before to do a long sum and not an int one

int a = 2147483647;
System.out.println(a + 1); //-2147483648

int b = 2147483647;
System.out.println(a + b); // -2

long c = a + (long) b; // or ((long) a) + b;
System.out.println(c); //4294967294

Unexpected output in Java while adding of two Integers

2 Answers2