Package org.apache.commons.collections

Class ComparatorUtils

java.lang.Object
org.apache.commons.collections.ComparatorUtils
public class ComparatorUtils extends Object
Provides convenient static utility methods for Comparator objects.

Most of the functionality in this class can also be found in the comparators package. This class merely provides a convenient central place if you have use for more than one class in the comparators subpackage.

Since:
Commons Collections 2.1
Version:
$Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
Author:
Paul Jack, Stephen Colebourne

  • Field Details

  • Constructor Details

    • ComparatorUtils

      public ComparatorUtils()
      ComparatorUtils should not normally be instantiated.

  • Method Details

    • naturalComparator

      public static Comparator naturalComparator()
      Gets a comparator that uses the natural order of the objects.
      Returns:
      a comparator which uses natural order

    • chainedComparator

      public static Comparator chainedComparator(Comparator comparator1, Comparator comparator2)
      Gets a comparator that compares using two Comparators.

      The second comparator is used if the first comparator returns equal.

      Parameters:
      comparator1 - the first comparator to use, not null
      comparator2 - the first comparator to use, not null
      Returns:
      a ComparatorChain formed from the two comparators
      Throws:
      NullPointerException - if either comparator is null
      See Also:

    • chainedComparator

      public static Comparator chainedComparator(Comparator[] comparators)
      Gets a comparator that compares using an array of Comparators, applied in sequence until one returns not equal or the array is exhausted.
      Parameters:
      comparators - the comparators to use, not null or empty or containing nulls
      Returns:
      a ComparatorChain formed from the input comparators
      Throws:
      NullPointerException - if comparators array is null or contains a null
      See Also:

    • chainedComparator

      public static Comparator chainedComparator(Collection comparators)
      Gets a comparator that compares using a collection of Comparators, applied in (default iterator) sequence until one returns not equal or the collection is exhausted.
      Parameters:
      comparators - the comparators to use, not null or empty or containing nulls
      Returns:
      a ComparatorChain formed from the input comparators
      Throws:
      NullPointerException - if comparators collection is null or contains a null
      ClassCastException - if the comparators collection contains the wrong object type
      See Also:

    • reversedComparator

      public static Comparator reversedComparator(Comparator comparator)
      Gets a comparator that reverses the order of the given comparator.
      Parameters:
      comparator - the comparator to reverse
      Returns:
      a comparator that reverses the order of the input comparator
      See Also:

    • booleanComparator

      public static Comparator booleanComparator(boolean trueFirst)
      Gets a Comparator that can sort Boolean objects.

      The parameter specifies whether true or false is sorted first.

      The comparator throws NullPointerException if a null value is compared.

      Parameters:
      trueFirst - when true, sort true Booleans before false Booleans.
      Returns:
      a comparator that sorts booleans

    • nullLowComparator

      public static Comparator nullLowComparator(Comparator comparator)
      Gets a Comparator that controls the comparison of null values.

      The returned comparator will consider a null value to be less than any nonnull value, and equal to any other null value. Two nonnull values will be evaluated with the given comparator.

      Parameters:
      comparator - the comparator that wants to allow nulls
      Returns:
      a version of that comparator that allows nulls
      See Also:

    • nullHighComparator

      public static Comparator nullHighComparator(Comparator comparator)
      Gets a Comparator that controls the comparison of null values.

      The returned comparator will consider a null value to be greater than any nonnull value, and equal to any other null value. Two nonnull values will be evaluated with the given comparator.

      Parameters:
      comparator - the comparator that wants to allow nulls
      Returns:
      a version of that comparator that allows nulls
      See Also:

    • transformedComparator

      public static Comparator transformedComparator(Comparator comparator, Transformer transformer)
      Gets a Comparator that passes transformed objects to the given comparator.

      Objects passed to the returned comparator will first be transformed by the given transformer before they are compared by the given comparator.

      Parameters:
      comparator - the sort order to use
      transformer - the transformer to use
      Returns:
      a comparator that transforms its input objects before comparing them
      See Also:

    • min

      public static Object min(Object o1, Object o2, Comparator comparator)
      Returns the smaller of the given objects according to the given comparator, returning the second object if the comparator returns equal.
      Parameters:
      o1 - the first object to compare
      o2 - the second object to compare
      comparator - the sort order to use
      Returns:
      the smaller of the two objects

    • max

      public static Object max(Object o1, Object o2, Comparator comparator)
      Returns the larger of the given objects according to the given comparator, returning the second object if the comparator returns equal.
      Parameters:
      o1 - the first object to compare
      o2 - the second object to compare
      comparator - the sort order to use
      Returns:
      the larger of the two objects