Comparators.comparing doesn't handle nulls (original) (raw)

Michael Nascimento misterm at gmail.com
Thu Apr 18 18:12:48 PDT 2013

Yes, Michael, that's precisely what I was referring to and I agree with your suggestions.

Regards, Michael

On Thu, Apr 18, 2013 at 8:40 PM, Michael Hixson <michael.hixson at gmail.com> wrote:

I believe he is talking about handling nulls within Comparator.compare(a, b). At the risk of beating a dead horse, I'll repeat something I suggested in the past. Either (A) or (B) below:

A) Extension methods on Comparator, like Guava: default Comparator nullsFirst() { ... } default Comparator nullsLast() { ... } B) Static methods on Comparators: public static Comparator nullsFirst() { ... } public static Comparator nullsLast() { ... } The first form would be easier to implement. The methods would return a modified version of the current comparator that permits null arguments to compare(a, b). The second form would be slightly harder to implement (~100 or so lines of code IIRC). The methods would return singletons that permit null arguments to compare(a, b). These singletons will have overridden implementations of whatever methods necessary to preserve null-safety throughout further chained calls to thenComparing(...) methods. For example: // Compare strings with nulls first and the rest in case-insensitive order. Comparator c = Comparators.nullsFirst() .thenComparing(String.CASEINSENSITIVEORDER); I personally prefer the second form (B). -Michael On Thu, Apr 18, 2013 at 3:50 PM, Henry Jen <henry.jen at oracle.com> wrote: Would you be more specific?

Comparators.comparing is not taking null as arguments. As how the returned Comparator compare nulls is really depends on Comparator itself. The Comparable style comparator won't handle null as Comparable doesn't support null. Cheers, Henry

On Apr 18, 2013, at 1:28 PM, Michael Nascimento <misterm at gmail.com> wrote: Hi guys, In most usages of Guava's ComparisonChain / Ordering that I am trying to replace with Comparator, nulls are involved. Comparators.comparing provides no easy way of handling this except by writing verbose code. Any plans to improve on that? Regards, Michael

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