Hashcode of an int

Question

What is the hashcode of a primitive type, such as int?

for example, let's say num was an interger.

int hasCode = 0;

if (num != 0) {
  hasCode = hasCode + num.hashCode();
}

Tetracycline

You can't call methods on primitives. Although it can be autoboxed, and then as an Integer (or similar) you'll get Integer.hashCode. – Crowded

In that case, we could be more helpful and add what the hashCodes would be for the wrapper classes. – Educt

The hashcode of an integer is the integer itself. – Marshamarshal

@DennisMeng Can you not read the API docs? – Crowded

I could, but the point of my comment was that we shouldn't shut the OP down just because of a minor technicality. The point of my comment was that we should probably be giving answers closer to the actual spirit of the problem. – Educt

Answer 1

For the hashCode of an int the most natural choice is to use the int itself. A better question is what to use for the hashCode of a long since it doesn't fit into the int-sized hashcode. Generally, your best source for that—and all hashCode-related questions—would be Effective Java.

Here's what Effective Java recommends (and the JDK uses) for the long type:

(int) (value ^ (value >>> 32))

Bingle

I got curious about the long hash code and have looked it up, it's: (int)(value ^ (value >>> 32)); – Getraer

@platzhirsch Yes, that's how it's implemented in java.lang.Long, and that's what Effective Java recommends. – Bingle

@MarkoTopolnik actually I think this is probably a lot more useful. – Mikesell

@veer You mean browsing through the JDK code? There will be no mention of a primitive type's hashcode there. Maybe you mean inspecting hashCode of primitive wrappers---in that case I'd recommend grepcode over the unwieldy download. – Bingle

Answer 2

Taken from the Integer.class source code:

/**
 * Returns a hash code for this {@code Integer}.
 *
 * @return  a hash code value for this object, equal to the
 *          primitive {@code int} value represented by this
 *          {@code Integer} object.
 */
public int hashCode() {
    return value;
}

Where value is the value of the integer.

Getraer

Note: It's correct but the question was meant for primitive int and not Integer object holding 'integer' value – Sanderson

Answer 3

No hashCode() method for primitive type int available.

Integer is Wrapper class type and hashcode() returns an int

Sandry

Answer 4

The java.lang.Integer.hashCode() method returns a hash code value for primitive value of int but represented as an Integer object.

/**
 * Returns a hash code value for an Integer,
 * equal to the primitive int value it represents.
 */
public class IntegerDemo {

    public static void main(String[] args){
        Integer i = new Integer("20");
        System.out.println("Value = " + i.hashCode());
    }

}`

Results:

Value = 20

Source Link: http://www.tutorialspoint.com/java/lang/integer_hashcode.htm

Driedup

the retval intermediary variable isn't really necessary in this code as it is only being used once. – Tamanaha