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
  Version:
    $Id: ComparatorUtils.java 1591832 2014-05-02 08:58:40Z tn $

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static Comparator` | `NATURAL_COMPARATOR` Comparator for natural sort order.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `static Comparator<Boolean>` | `booleanComparator(boolean trueFirst)` Gets a Comparator that can sort Boolean objects.
    `static <E> Comparator<E>` | `chainedComparator(Collection<Comparator<E>> comparators)` Gets a comparator that compares using a collection of `Comparator`s, applied in (default iterator) sequence until one returns not equal or the collection is exhausted.
    `static <E> Comparator<E>` | `chainedComparator(Comparator<E>... comparators)` Gets a comparator that compares using an array of `Comparator`s, applied in sequence until one returns not equal or the array is exhausted.
    `static <E> E` | `max(E o1, E o2, Comparator<E> comparator)` Returns the larger of the given objects according to the given comparator, returning the second object if the comparator returns equal.
    `static <E> E` | `min(E o1, E o2, Comparator<E> comparator)` Returns the smaller of the given objects according to the given comparator, returning the second object if the comparator returns equal.
    `static <E extends Comparable<? super E>> Comparator<E>` | `naturalComparator()` Gets a comparator that uses the natural order of the objects.
    `static <E> Comparator<E>` | `nullHighComparator(Comparator<E> comparator)` Gets a Comparator that controls the comparison of `null` values.
    `static <E> Comparator<E>` | `nullLowComparator(Comparator<E> comparator)` Gets a Comparator that controls the comparison of `null` values.
    `static <E> Comparator<E>` | `reversedComparator(Comparator<E> comparator)` Gets a comparator that reverses the order of the given comparator.
    `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.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### NATURAL_COMPARATOR

          public static final Comparator NATURAL_COMPARATOR

      Comparator for natural sort order.
      See Also:
        `ComparableComparator.comparableComparator()`

  - ### Method Detail

    - #### 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

    - #### chainedComparator

          public static <E> Comparator<E> chainedComparator(Comparator<E>... comparators)

      Gets a comparator that compares using an array of `Comparator`s, 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:
        `ComparatorChain`

    - #### chainedComparator

          public static <E> Comparator<E> chainedComparator(Collection<Comparator<E>> comparators)

      Gets a comparator that compares using a collection of `Comparator`s, 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:
        `ComparatorChain`

    - #### 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:
        `ReverseComparator`

    - #### 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` `Boolean`s before `false` `Boolean`s.
      Returns:
        a comparator that sorts booleans

    - #### 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:
        `NullComparator`

    - #### 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:
        `NullComparator`

    - #### 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:
        `TransformingComparator`

    - #### min

          public static <E> E min(E o1,
                  E o2,
                  Comparator<E> comparator)

      Returns the smaller 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

    - #### max

          public static <E> E max(E o1,
                  E o2,
                  Comparator<E> comparator)

      Returns the larger 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

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