org.springframework.util.comparator
Class NullSafeComparator<T>

java.lang.Object
  org.springframework.util.comparator.NullSafeComparator<T>

All Implemented Interfaces:

java.util.Comparator<T>

public class NullSafeComparator<T>
extends java.lang.Object
implements java.util.Comparator<T>

A Comparator that will safely compare nulls to be lower or higher than other objects. Can decorate a given Comparator or work on Comparables.

Since:

1.2.2

Author:

Keith Donald, Juergen Hoeller

See Also:

Comparable

Field Summary

private java.util.Comparator<T>	nonNullComparator
static NullSafeComparator	NULLS_HIGH A shared default instance of this comparator, treating nulls higher than non-null objects.
static NullSafeComparator	NULLS_LOW A shared default instance of this comparator, treating nulls lower than non-null objects.
private boolean	nullsLow

Constructor Summary

private	NullSafeComparator(boolean nullsLow) Create a NullSafeComparator that sorts null based on the provided flag, working on Comparables.
	NullSafeComparator(java.util.Comparator<T> comparator, boolean nullsLow) Create a NullSafeComparator that sorts null based on the provided flag, decorating the given Comparator.

Method Summary

int	compare(T o1, T o2)
boolean	equals(java.lang.Object obj)
int	hashCode()
java.lang.String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

NULLS_LOW

public static final NullSafeComparator NULLS_LOW

A shared default instance of this comparator, treating nulls lower than non-null objects.

NULLS_HIGH

public static final NullSafeComparator NULLS_HIGH

A shared default instance of this comparator, treating nulls higher than non-null objects.

nonNullComparator

private final java.util.Comparator<T> nonNullComparator

nullsLow

private final boolean nullsLow

Constructor Detail

NullSafeComparator

private NullSafeComparator(boolean nullsLow)

Create a NullSafeComparator that sorts null based on the provided flag, working on Comparables.

When comparing two non-null objects, their Comparable implementation will be used: this means that non-null elements (that this Comparator will be applied to) need to implement Comparable.

As a convenience, you can use the default shared instances: NullSafeComparator.NULLS_LOW and NullSafeComparator.NULLS_HIGH.

Parameters:

nullsLow - whether to treat nulls lower or higher than non-null objects

See Also:

Comparable, NULLS_LOW, NULLS_HIGH

NullSafeComparator

public NullSafeComparator(java.util.Comparator<T> comparator,
                          boolean nullsLow)

Create a NullSafeComparator that sorts null based on the provided flag, decorating the given Comparator.

When comparing two non-null objects, the specified Comparator will be used. The given underlying Comparator must be able to handle the elements that this Comparator will be applied to.

Parameters:

comparator - the comparator to use when comparing two non-null objects

nullsLow - whether to treat nulls lower or higher than non-null objects

Method Detail

compare

public int compare(T o1,
                   T o2)

Specified by:

compare in interface java.util.Comparator<T>

equals

public boolean equals(java.lang.Object obj)

Specified by:

equals in interface java.util.Comparator<T>

Overrides:

equals in class java.lang.Object

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object