org.apache.commons.collections.comparators

Class NullComparator

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: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $

Author: Michael A. Smith

Constructor Summary
NullComparator()
Construct an instance that sorts null higher than any non-null object it is compared with.
NullComparator(Comparator nonNullComparator)
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 nonNullComparator, boolean nullsAreHigh)
Construct an instance that sorts null higher or lower than any non-null object it is compared with.
Method Summary
intcompare(Object o1, Object o2)
Perform a comparison between two objects.
booleanequals(Object obj)
Determines whether the specified object represents a comparator that is equal to this comparator.
inthashCode()
Implement a hash code for this comparator that is consistent with equals.

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.

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.

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.

Returns: a hash code for this comparator.

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