equals and hashCode Generation

Recently we discussed equals() and hashCode() implementations. A proper implementation is not trivial, as "father" Bloch showed us years ago. Back in 2004 I wrote a plugin for Eclipse 2 to generate these methods. (Unfortunately I never managed to publish it. I know I am weak ;-) My home grown solution would produce something like

public int hashCode() {
  long bits;
  int result = 17;
  result = 37 * result + (aBoolean ? 1231 : 1237);
  result = 37 * result + (int)
    ((bits = Double.doubleToLongBits(aDouble)) ^ (bits >> 32));
  result = 37 * result + (int) (aLong ^ (aLong >> 32));
  result = 37 * result + anInt;
  if (anObject != null) {
    result = 37 * result + anObject.hashCode();
  }
  if (anArray != null) {
    result = 37 * result + anArray.hashCode();
  }
  return result;
}
public boolean equals(Object obj) {
  if (this == obj) {
    return true;
  }
  else if (obj == null || getClass() != obj.getClass()) {
    return false;
  }
  final Homegrown o = (Homegrown) obj;
  return (aBoolean == o.aBoolean &&
         aDouble == o.aDouble &&
         aLong == o.aLong &&
         anInt == o.anInt &&
         (anObject == o.anObject ||
           (anObject != null && anObject.equals(o.anObject))) &&
         (anArray == o.anArray ||
           (anArray != null && anArray.equals(o.anArray))));
}

I know, I know the implementation for arrays is most likely not what you want. (Did I say that I am weak? :-) Since Java 5 one could use the java.util.Arrays class to fix it. Nevertheless, it served me well for some years. There are several other plugins for Eclipse, and Scott McMaster wrote about in 2006. Since version 3.3 (Europa) Eclipse can finally do it on its own:

public int hashCode() {
  final int prime = 31;
  int result = 1;
  result = prime * result + (aBoolean ? 1231 : 1237);
  long temp;
  temp = Double.doubleToLongBits(aDouble);
  result = prime * result + (int) (temp ^ (temp >>> 32));
  result = prime * result + (int) (aLong ^ (aLong >>> 32));
  result = prime * result + anInt;
  result = prime * result +
                   ((anObject == null) ? 0 : anObject.hashCode());
  result = prime * result + Arrays.hashCode(anArray);
  return result;
}
public boolean equals(Object obj) {
  if (this == obj) {
    return true;
  }
  if (obj == null) {
    return false;
  }
  if (getClass() != obj.getClass()) {
    return false;
  }
  final Eclipse33Java5 other = (Eclipse33Java5) obj;
  if (aBoolean != other.aBoolean) {
    return false;
  }
  if (Double.doubleToLongBits(aDouble) !=
      Double.doubleToLongBits(other.aDouble)) {
    return false;
  }
  if (aLong != other.aLong) {
    return false;
  }
  if (anInt != other.anInt) {
    return false;
  }
  if (anObject == null) {
    if (other.anObject != null) {
      return false;
    }
  }
  else if (!anObject.equals(other.anObject)) {
    return false;
  }
  if (!Arrays.equals(anArray, other.anArray)) {
    return false;
  }
  return true;
}

Using the ternary operator the hashCode method gets quite compact, but equals is a bit too verbose for my liking. IntelliJ IDEA could always generate these methods. IDEA 7.0 creates something like

public int hashCode() {
  int result;
  long temp;
  result = (aBoolean ? 1 : 0);
  temp = aDouble != +0.0d ? Double.doubleToLongBits(aDouble) : 0L;
  result = 31 * result + (int) (temp ^ (temp >>> 32));
  result = 31 * result + (int) (aLong ^ (aLong >>> 32));
  result = 31 * result + anInt;
  result = 31 * result +
                (anObject != null ? anObject.hashCode() : 0);
  result = 31 * result +
                (anArray != null ? Arrays.hashCode(anArray) : 0);
  return result;
}
public boolean equals(Object o) {
  if (this == o) {
    return true;
  }
  if (o == null || getClass() != o.getClass()) {
    return false;
  }
  Idea70Java5 original = (Idea70Java5) o;
  if (aBoolean != original.aBoolean) {
    return false;
  }
  if (Double.compare(original.aDouble, aDouble) != 0) {
    return false;
  }
  if (aLong != original.aLong) {
    return false;
  }
  if (anInt != original.anInt) {
    return false;
  }
  if (anObject != null ? !anObject.equals(original.anObject) :
                         original.anObject != null) {
    return false;
  }
  // Probably incorrect - comparing Object[] with Arrays.equals
  if (!Arrays.equals(anArray, original.anArray)) {
    return false;
  }
  return true;
}

Typical IDEA, with a little fix for +0.0/-0.0 and some warning concerning Arrays.equals, but else totally the same. In fact, all these implementations suck (including my own, which sucks most). All these result = prime * result ... and if ... return false; are definitely not DRY. I always favour Apache Commons Lang builders. A hand-coded solution using them would look like

public int hashCode() {
  return new HashCodeBuilder().
         append(aBoolean).
         append(aDouble).
         append(aLong).
         append(anInt).
         append(anObject).toHashCode();
}
public boolean equals(Object other) {
  if (this == other) {
    return true;
  }
  if (other == null || getClass() != other.getClass()) {
    return false;
  }
  ApacheCommons o = (ApacheCommons) other;
  return new EqualsBuilder().
         append(aBoolean, o.aBoolean).
         append(aDouble, o.aDouble).
         append(aLong, o.aLong).
         append(anInt, o.anInt).
         append(anObject, o.anObject).
         append(anArray, o.anArray).isEquals();
}

Well, that's much shorter, isn't it.