why Integer.MAX_VALUE + 1 == Integer.MIN_VALUE?

java integer integer-overflow twos-complement jls
Oleg Mikheev picture Oleg Mikheev · Feb 22, 2012 · Viewed 39.1k times · Source

System.out.println(Integer.MAX_VALUE + 1 == Integer.MIN_VALUE);

is true.

I understand that integer in Java is 32 bit and can't go above 231-1, but I can't understand why adding 1 to its MAX_VALUE results in MIN_VALUE and not in some kind of exception. Not mentioning something like transparent conversion to a bigger type, like Ruby does.

Is this behavior specified somewhere? Can I rely on it?

Answer

Bozho picture Bozho · Feb 22, 2012

Because the integer overflows. When it overflows, the next value is Integer.MIN_VALUE. Relevant JLS

If an integer addition overflows, then the result is the low-order bits of the mathematical sum as represented in some sufficiently large two's-complement format. If overflow occurs, then the sign of the result is not the same as the sign of the mathematical sum of the two operand values.

Related questions

How does Java handle integer underflows and overflows and how would you check for it?

How does Java handle integer underflows and overflows? Leading on from that, how would you check/test that this is occurring?

Read More
How can I detect integer overflow on 32 bits int?

I know such topic was asked several times, but my question is about overflow on full 32 bits of int. For example: 11111111111111111111111111111111 + 00000000000000000000000000000001 = 00000000000000000000000000000000 //overflow! I found topic with similar question about this, however the algorithm is not perfect. 11111111111111111111111111111111 + 00000000000000000000000000000000 = 00000000000000000000000000000000 //overflow! Is there any …

Read More
Why does Java think that the product of all numbers from 10 to 99 is 0?

The following block of codes gives the output as 0. public class HelloWorld{ public static void main(String []args){ int product = 1; for (int i = 10; i <= 99; i++) { product *= i; } System.out.println(product); } } Please can somebody explain why this happens?

Read More