Hash code uniqueness for string variable

Question

in my Event class, it has a name variable as a String, and I want the name to be the unique identifier of an object. In implementing the hashCode() method, which way is recommended or right?

@Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((name == null) ? 0 : name.hashCode());
    return result;
}

or

@Override
public int hashCode() {
    return name != null ? name.hashCode() : 0;
}

first hashcode == second hashcode + 31. What's the point?

Andres F.
– Andres F.

2014-09-15 01:57:03 +00:00
Commented Sep 15, 2014 at 1:57 — Andres F.
– Andres F., Commented Sep 15, 2014 at 1:57

nneonneo · Accepted Answer · 2014-09-15 01:48:19Z

3

You may as well just use the default Java hashCode since it works well enough for most purposes. Don't overcomplicate: the second, simpler function will work just fine.

answered Sep 15, 2014 at 1:48

nneonneo

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Comments

Dici · Accepted Answer · 2014-09-15 01:50:49Z

1

The first one is a template when there are many attributes (possibly of various types), but if you only have a String the default hashCode() defined on String (inherited from Object) will do fine.

answered Sep 15, 2014 at 1:50

Dici

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2 Comments

marlon Over a year ago

I have more fields, like boolean, and Long, but the String "name" is going to be the natural and unique identifier.

Dici Over a year ago

Yes that's what I meant, then the second one is indeed the most appropriate.

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