Module com.github.f4b6a3.uuid

Package com.github.f4b6a3.uuid.util

Class UuidComparator

java.lang.Object

com.github.f4b6a3.uuid.util.UuidComparator

All Implemented Interfaces:

Comparator<UUID>

public final class UuidComparator
extends Object
implements Comparator<UUID>

Comparator for UUIDs.

The default static method compares two time-based UUIDs by comparing the time stamps first and then comparing the least significant bits as unsigned 64-bit integers. If both UUIDs are not time-based then it compares them as unsigned 128-bit integers.

The opaque static method compares two UUIDs as unsigned 128-bit integers. It's the same as lexicographic sorting of UUID canonical strings.

Constructor Summary

Constructors

Constructor	Description
UuidComparator()	Creates a default implementation of UuidComparator.

Method Summary

Modifier and Type	Method	Description
int	compare(UUID uuid1, UUID uuid2)	Compares two UUIDs.
static int	defaultCompare(UUID uuid1, UUID uuid2)	Compares two UUIDs.
static UuidComparator	getDefaultInstance()	Returns a default implementation of UuidComparator.
static UuidComparator	getOpaqueInstance()	Returns an opaque implementation of UuidComparator.
static int	opaqueCompare(UUID uuid1, UUID uuid2)	Compares two UUIDs.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.util.Comparator

equals, reversed, thenComparing, thenComparing, thenComparing, thenComparingDouble, thenComparingInt, thenComparingLong

Constructor Detail

UuidComparator

public UuidComparator()

Creates a default implementation of UuidComparator.

See Also:

defaultCompare(UUID, UUID)

Method Detail

getDefaultInstance

public static UuidComparator getDefaultInstance()

Returns a default implementation of UuidComparator.

Returns:

a UuidComparator

See Also:

defaultCompare(UUID, UUID)

getOpaqueInstance

public static UuidComparator getOpaqueInstance()

Returns an opaque implementation of UuidComparator.

Returns:

a opaque UuidComparator

See Also:

opaqueCompare(UUID, UUID)

defaultCompare

public static int defaultCompare(UUID uuid1,
                                 UUID uuid2)

Compares two UUIDs.

The default static method compares two time-based UUIDs by comparing the time stamps first and then comparing the least significant bits as unsigned 64-bit integers. If both UUIDs are not time-based then it compares them as unsigned 128-bit integers.

The first of two UUIDs is greater than the second if the time stamp is greater for the first UUID. If the time stamps are equal, the first of two UUIDs is greater than the second if the most significant byte in which they differ is greater for the first UUID.

It can be useful for these reasons:

1. UUID.compareTo(UUID) doesn't work well for time-based UUIDs;
2. UUID.compareTo(UUID) can lead to unexpected behavior due to signed long comparison;
3. UUID.compareTo(UUID) throws NullPointerException if a null UUID is given.

Parameters:

uuid1 - a UUID

uuid2 - another UUID

Returns:

-1, 0 or 1 as u1 is less than, equal to, or greater than u2

opaqueCompare

public static int opaqueCompare(UUID uuid1,
                                UUID uuid2)

Compares two UUIDs.

The opaque static method compares two UUIDs as unsigned 128-bit integers. It's the same as lexicographic sorting of UUID canonical strings.

The first of two UUIDs is greater than the second if the most significant byte in which they differ is greater for the first UUID.

The opaque method is faster than the default method as it does not check the UUID version.

It's referred to as "opaque" just because it works like a "blind byte-to-byte comparison".

It can be useful for these reasons:

1. UUID.compareTo(UUID) can lead to unexpected behavior due to signed long comparison;
2. UUID.compareTo(UUID) throws NullPointerException if a null UUID is given.

Parameters:

uuid1 - a UUID

uuid2 - another UUID

Returns:

-1, 0 or 1 as u1 is less than, equal to, or greater than u2

compare

public int compare(UUID uuid1,
                   UUID uuid2)

Compares two UUIDs.

Specified by:

compare in interface Comparator<UUID>

Parameters:

uuid1 - a UUID

uuid2 - another UUID

Returns:

-1, 0 or 1 as u1 is less than, equal to, or greater than u2

See Also:

defaultCompare(UUID, UUID)