Java Inconsistent Logic Multiplying Hashcodes

Question

I'm new to Java, and trying to translate this code into SQL:

public class hashtest {

    public static void main(String []args) {
        calculateHashCode("asdf","asdf","asdf");
    }

    public static int calculateHashCode(String a, String b, String c) {
        final int prime = 31;
        int result = 1;

        result = prime * result + ((a == null) ? 0 : a.hashCode());
        System.out.println(result);
        result = prime * result + ((b == null) ? 0 : b.hashCode());
        System.out.println(result);
        result = prime * result + ((c == null) ? 0 : c.hashCode());
        System.out.println(result);

        System.out.println(a.hashCode());
        System.out.println(b.hashCode());
        System.out.println(c.hashCode());
        return result;
    }
}

How is it that the value of the result variable flips from positive to negative in the final statement, when all hashcode values are positive?

OUTPUT

I executed this code on (https://www.tutorialspoint.com/compile_java_online.php)

"when all hashcode values are positive?" nothing says that hashcodes have to be positive. But, overflow. — Andy Turner, Sep 18 '18 at 11:32
@Pops Do you know the range of the int in java? And what happen when it exceeds — mallikarjun, Sep 18 '18 at 11:35

score 1 · Answer 1 · answered Sep 18 '18 at 11:35

1

The multiplication result overflows, continues from the minimum value of int which is -2147483648, giving you a negative result.

answered Sep 18 '18 at 11:35

S.K.

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score 0 · Answer 2 · answered Sep 18 '18 at 11:34

0

The multiplication overflows.

If you change the type of result to long (but cast back at the end, of course), you get the output:

Ideone demo

2982449683 is greater than Integer.MAX_VALUE.

answered Sep 18 '18 at 11:34

Andy Turner

137,514
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Java Inconsistent Logic Multiplying Hashcodes

2 Answers2