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From: v_borchert@despammed.com (Volker Borchert)
Newsgroups: comp.lang.java.programmer
Subject: Re: verbose sort
Date: 2 Aug 2012 21:38:17 GMT
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Eric Sosman wrote:
>   To: bob smith
> From: Eric Sosman <esosman@ieee-dot-org.invalid>
> 
> On 8/2/2012 11:37 AM, bob smith wrote:
> > I have some code that sorts a list like so:
> >
> > Vector<String> my_list = new Vector<String>();
> >
> >
> >               Comparator<String> c = new Comparator<String>() {
> >                       @Override
> >                       public int compare(String object1, String object2) {
> >                               if (object1 == null)
> >                                       return -1;
> >                               if (object2 == null)
> >                                       return 1;
> >                               object1 = object1.toLowerCase();
> >                               object2 = object2.toLowerCase();
> >                               return object1.compareTo(object2);
> >                       };
> >               };
> >
> > Collections.sort(my_list, c);
> >
> >
> > This seems like a lot of code for such a common operation.  Is there a more
> succinct way of doing this?
> 
>      Consider using compareToIgnoreCase().  Also, think about what
> happens when two null's are compared: You should return zero rather than 
> declaring one of them "less than" the other, because otherwise your comparator 
> is inconsistent (you can have A<B, B<C, but C<A).
> 
>         public int compare(String s1, String s2) {
>             if (s1 == null)
>                 return s2 == null ? 0 : -1;
>             return s2 == null ? +1 : s1.compareToIgnoreCase(s2);
>         }

I'd do it as a fastpath and GoF Decorator

public final class NullFirstComparator<T> implements Comparator<T> {
  @NonNull
  private final Comparator<T> delegate;

  public NullFirstComparator(@NonNull final Comparator<T> delegate) {
    this.delegate = delegate;
  }

  public int compare(final T t1, final T t2) {
    if (t1 == t2) {
      return 0;
    } else if (t1 == null) {
      return -1;
    } else if (t2 == null) {   
      return 1;
    } else {
      return delegate.compare(t1, t2);
    }
  }
}

Collections.sort(my_list, new NullFirstComparator<String>(String.CASE_INSENSITIVE_ORDER));

-- 

"I'm a doctor, not a mechanic." Dr Leonard McCoy <mccoy@ncc1701.starfleet.fed>
"I'm a mechanic, not a doctor." Volker Borchert  <v_borchert@despammed.com>