Package org.apache.commons.collections.comparators

Class NullComparator

  • All Implemented Interfaces:
    Serializable, Comparator
    public class NullComparator
extends Object
implements Comparator, Serializable
    A Comparator that will compare nulls to be either lower or higher than other objects.
    Since:
    Commons Collections 2.0
    Version:
    $Revision: 647116 $ $Date: 2008-04-11 13:23:08 +0200 (Fri, 11 Apr 2008) $
    Author:
    Michael A. Smith
    See Also:
    Serialized Form

    • Constructor Detail

      • 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​(Comparator 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​(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 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 Detail

      • compare

        public int compare​(Object o1,
                   Object 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
        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.

      • 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.

      • 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
        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.