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

Fields

Modifier and Type	Field and Description
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

Constructors

Modifier	Constructor and Description
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

Modifier and Type	Method and Description
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

Methods inherited from interface java.util.Comparator

comparing, comparing, comparingDouble, comparingInt, comparingLong, naturalOrder, nullsFirst, nullsLast, reversed, reverseOrder, thenComparing, thenComparing, thenComparing, thenComparingDouble, thenComparingInt, thenComparingLong

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