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Sorting a collection

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For more info, see http://mindprod.com/jgloss/sort.html .

Example #1

Say we want to sort a family of bitsets in ascending order by size.

Vector<BitSet> set = ...;

Collections.sort(set, new BitsetComparatorBySize());

// ==============================

class BitsetComparatorBySize 
implements Comparator<BitSet>
{
   // compare two Bitsets (callback for sort)
   // Effectively returns a-b; e.g. 
   // +1 (or any positive number) if a > b
   // 0 if a == b
   // -1 (or any negative number) if a < b
   public final int compare(BitSet a, BitSet b) {
      return ( ((BitSet) a).cardinality() - ((BitSet) b).cardinality() );
   } // end compare
}

Or, compare two BitSets lexicographically:

public class BitsetComparer 
implements Comparator<Object> 
{
   public int compare(Object o1, Object o2) {
      return (((BitSet) o1).toString().compareTo(((BitSet) o2).toString()));
   }
}

Example #2

If you have your own class, you can define how to compare two objects of this class.

public class HashElem
implements Comparable<Object>
{
   ...

   public int compareTo(Object o)
   {
      if (o==null || !(o instanceof HashElem)) {
         throw new ClassCastException();
      }
      return (this.intent.toString().compareTo(((HashElem) o).getIntent().toString()));
   }

} // eof class