Why 10000000*1000 giving 1410065408 in java?

Question

class a {
    public static void main(String arg[]){
        int a=10000000;
        int b=1000;
        int c=a*b;
        System.out.println(c);
    }
}

The output is 1410065408. Can anyone help to justify it?

Answer 1

Here is a tiny example what is actually happening, by using a loop. You will notice that the multiplication and the loop reduce the same result. Basicly this is happening because the multiplication exceeds the limit of Integer.MAX_VALUE. If this limit is overflown, which means the calculated number is greater then this specific value, then your number will be equal to Integer.MIN_VALUE+theRestOfTheNumber and the calculation will be going on with this number.

public static void main(String[] args) {
    final int start_value = 10000000;
    final int multiplier = 1000;
    int result1 = 0, result2 = 0;
    for(int i = 0;i<1000;++i) {
        result1 += start_value;
        if(result1 < 0) {
            System.out.println("Overflow happend, starting at Integer.MIN_VALUE " + Integer.MIN_VALUE + " again. You did exceed the number " + Integer.MAX_VALUE);
        }
    }
    result2 = start_value * multiplier;
    System.out.println("RESULT1: " + result1);
    System.out.println("RESULT2: " + result2);
}

O/P

Overflow happend, starting at Integer.MIN_VALUE -2147483648 again. You did exceed the number 2147483647
Overflow happend, starting at Integer.MIN_VALUE -2147483648 again. You did exceed the number 2147483647
Overflow happend, starting at Integer.MIN_VALUE -2147483648 again. You did exceed the number 2147483647
// MANY MANY MORE OVERFLOWS, 429 to be exact.
Overflow happend, starting at Integer.MIN_VALUE -2147483648 again. You did exceed the number 2147483647
RESULT1: 1410065408
RESULT2: 1410065408