Package org.apache.commons.collections4.comparators

# Class NullComparator<E>

java.lang.Object
org.apache.commons.collections4.comparators.NullComparator<E>

Type Parameters:
  `E` - the type of objects compared by this comparator

All Implemented Interfaces:
  `Serializable`, `Comparator<E>`

public class NullComparator<E> extends Object implements Comparator<E>, Serializable
A Comparator that will compare nulls to be either lower or higher than other objects.

Since:
  2.0
See Also:
  - Serialized Form

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `NullComparator()`
  Construct an instance that sorts `null` higher than any non-`null` object it is compared with.
  `NullComparator(boolean nullsAreHigh)`
  Construct an instance that sorts `null` higher or lower than any non-`null` object it is compared with.
  `NullComparator(Comparator<? super E> nonNullComparator)`
  Construct an instance that sorts `null` higher than any non-`null` object it is compared with.
  `NullComparator(Comparator<? super E> nonNullComparator, boolean nullsAreHigh)`
  Construct an instance that sorts `null` higher or lower than any non-`null` object it is compared with.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `int`
  `compare(E o1, E o2)`
  Perform a comparison between two objects.
  `boolean`
  `equals(Object obj)`
  Determines whether the specified object represents a comparator that is equal to this comparator.
  `int`
  `hashCode()`
  Implement a hash code for this comparator that is consistent with `equals(Object)`.

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

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

  ### Methods inherited from interface java.util.Comparator

  `reversed, thenComparing, thenComparing, thenComparing, thenComparingDouble, thenComparingInt, thenComparingLong`

- ## Constructor Details

  - ### NullComparator

    public NullComparator()
    Construct an instance that sorts `null` higher than any non-`null` object it is compared with. When comparing two non-`null` objects, the `ComparableComparator` is used.

  - ### NullComparator

    public NullComparator(boolean nullsAreHigh)
    Construct an instance that sorts `null` higher or lower than any non-`null` object it is compared with. When comparing two non-`null` objects, the `ComparableComparator` is used.
    Parameters:
      `nullsAreHigh` - a `true` value indicates that `null` should be compared as higher than a non-`null` object. A `false` value indicates that `null` should be compared as lower than a non-`null` object.

  - ### NullComparator

    public NullComparator(Comparator<? super E> nonNullComparator)
    Construct an instance that sorts `null` higher than any non-`null` object it is compared with. When comparing two non-`null` objects, the specified `Comparator` is used.
    Parameters:
      `nonNullComparator` - the comparator to use when comparing two non-`null` objects. This argument cannot be `null`
    Throws:
      `NullPointerException` - if `nonNullComparator` is `null`

  - ### NullComparator

    public NullComparator(Comparator<? super E> nonNullComparator, boolean nullsAreHigh)
    Construct an instance that sorts `null` higher or lower than any non-`null` object it is compared with. When comparing two non-`null` objects, the specified `Comparator` is used.
    Parameters:
      `nonNullComparator` - the comparator to use when comparing two non-`null` objects. This argument cannot be `null`
      `nullsAreHigh` - a `true` value indicates that `null` should be compared as higher than a non-`null` object. A `false` value indicates that `null` should be compared as lower than a non-`null` object.
    Throws:
      `NullPointerException` - if `nonNullComparator` is `null`

- ## Method Details

  - ### compare

    public int compare(E o1, E o2)
    Perform a comparison between two objects. If both objects are `null`, a `0` value is returned. If one object is `null` and the other is not, the result is determined on whether the Comparator was constructed to have nulls as higher or lower than other objects. If neither object is `null`, an underlying comparator specified in the constructor (or the default) is used to compare the non-`null` objects.
    Specified by:
      `compare` in interface `Comparator<E>`
    Parameters:
      `o1` - the first object to compare
      `o2` - the object to compare it to.
    Returns:
      `-1` if `o1` is "lower" than (less than, before, etc.) `o2`; `1` if `o1` is "higher" than (greater than, after, etc.) `o2`; or `0` if `o1` and `o2` are equal.

  - ### equals

    public boolean equals(Object obj)
    Determines whether the specified object represents a comparator that is equal to this comparator.
    Specified by:
      `equals` in interface `Comparator<E>`
    Overrides:
      `equals` in class `Object`
    Parameters:
      `obj` - the object to compare this comparator with.
    Returns:
      `true` if the specified object is a NullComparator with equivalent `null` comparison behavior (i.e. `null` high or low) and with equivalent underlying non-`null` object comparators.

  - ### hashCode

    public int hashCode()
    Implement a hash code for this comparator that is consistent with `equals(Object)`.
    Overrides:
      `hashCode` in class `Object`
    Returns:
      a hash code for this comparator.