Package org.apache.commons.collections4

Class ComparatorUtils

java.lang.Object
org.apache.commons.collections4.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:
2.1

  • Field Details

  • Method Details

    • booleanComparator

      public static Comparator<Boolean> 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

    • chainedComparator

      public static <E> Comparator<E> chainedComparator(Collection<Comparator<E>> 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.
      Type Parameters:
      E - the object type to compare
      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:

    • chainedComparator

      public static <E> Comparator<E> chainedComparator(Comparator<E>... comparators)
      Gets a comparator that compares using an array of Comparators, applied in sequence until one returns not equal or the array is exhausted.
      Type Parameters:
      E - the object type to compare
      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:

    • max

      public static <E> E max(E o1, E o2, Comparator<E> comparator)
      Returns the largest of the given objects according to the given comparator, returning the second object if the comparator returns equal.
      Type Parameters:
      E - the object type to compare
      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

    • min

      public static <E> E min(E o1, E o2, Comparator<E> comparator)
      Returns the smallest of the given objects according to the given comparator, returning the second object if the comparator returns equal.
      Type Parameters:
      E - the object type to compare
      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

    • naturalComparator

      public static <E extends Comparable<? super E>> Comparator<E> naturalComparator()
      Gets a comparator that uses the natural order of the objects.
      Type Parameters:
      E - the object type to compare
      Returns:
      a comparator which uses natural order

    • nullHighComparator

      public static <E> Comparator<E> nullHighComparator(Comparator<E> 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.

      Type Parameters:
      E - the object type to compare
      Parameters:
      comparator - the comparator that wants to allow nulls
      Returns:
      a version of that comparator that allows nulls
      See Also:

    • nullLowComparator

      public static <E> Comparator<E> nullLowComparator(Comparator<E> 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.

      Type Parameters:
      E - the object type to compare
      Parameters:
      comparator - the comparator that wants to allow nulls
      Returns:
      a version of that comparator that allows nulls
      See Also:

    • reversedComparator

      public static <E> Comparator<E> reversedComparator(Comparator<E> comparator)
      Gets a comparator that reverses the order of the given comparator.
      Type Parameters:
      E - the object type to compare
      Parameters:
      comparator - the comparator to reverse
      Returns:
      a comparator that reverses the order of the input comparator
      See Also:

    • transformedComparator

      public static <I, O> Comparator<I> transformedComparator(Comparator<O> comparator, Transformer<? super I,? extends O> 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.

      Type Parameters:
      I - the input object type of the transformed comparator
      O - the object type of the decorated 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: