Question

If I have a simple Groovy class such as

class Address {

  Integer streetNumber
  String streetName
  String state
  String zip
  Country country    
}

Although I could write (or use an IDE to generate) hashCode and equals methods like:

boolean equals(o) {
    if (this.is(o)) return true;

    if (!o || getClass() != o.class) return false;

    Address that = (Address) o;

    if (streetNumber? !streetNumber.equals(that.streetNumber) : that.streetNumber!= null) return false;
    if (streetName? !streetName.equals(that.streetName) : that.streetName!= null) return false;
    if (state? !state.equals(that.state) : that.state!= null) return false;
    if (zip? !zip.equals(that.zip) : that.zip!= null) return false;
    if (country? !zip.equals(that.zip) : that.zip!= null) return false;

    return true;
}

int hashCode() {
    int result = (streetNumber ? streetNumber.hashCode() : 0);
    result = 31 * result + (streetName ? streetName.hashCode() : 0);
    result = 31 * result + (state ? state.hashCode() : 0);
    result = 31 * result + (zip ? zip.hashCode() : 0);
    return 31 * result + (country ? country.hashCode() : 0);
}

Although this will work fine, I feel I could be making better use of Groovy’s dynamism to achieve the same thing in a lot less code. One approach that springs to mind is using .properties to get a map of an object’s property names and values. I can then iterate over these properties, calling hashCode() or equals() on each one to achieve the same result as above.

Before I go down this path, I just want to check whether anyone else has found a good solution to this problem. I’m a bit wary of rolling my own solution, because the consequences of messing up equals() or hashCode() are potentially dire and hard to track down.

Thanks,
Don

Answer 1

I’m not a groovy developer, but I understood that from groovy 1.8 you can invoke the AST transformation using @EqualsAndHashCode on the type.