javolution.util

Class FastComparator<T>

Object

FastComparator<T>

All Implemented Interfaces:

Serializable, Comparator<T>, XMLSerializable

public abstract class FastComparator<T>
extends Object
implements Comparator<T>, XMLSerializable

This class represents a comparator to be used for equality as well as for ordering; instances of this class provide a hashcode function consistent with equal (if two objects are equal, they have the same hashcode), equality with null values is supported.

FastComparator can be employed with FastMap (e.g. custom key comparators for identity maps, value retrieval using keys of a different class that the map keys) or with FastCollection classes.

Version:

5.3, April 23, 2009

Author:

Jean-Marie Dautelle

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static FastComparator<Object>	DEFAULT Holds the default object comparator; rehash is performed if the system hash code (platform dependent) is not evenly distributed.
static FastComparator<Object>	DIRECT Holds the direct object comparator; no rehash is performed.
static FastComparator<Object>	IDENTITY Holds the identity comparator; poorly distributed system hashcodes are rehashed.
static FastComparator<CharSequence>	LEXICAL Holds a lexicographic comparator for any CharSequence or String instances.
static FastComparator<Object>	REHASH Holds the comparator for objects with uneven hash distribution; objects hashcodes are rehashed.
static Configurable<Boolean>	REHASH_SYSTEM_HASHCODE Indicates if the system hash code should be rehashed (see Javolution Configuration for details).
static FastComparator<String>	STRING Holds a fast comparator for java.lang.String.

Constructor Summary

Constructors

Constructor and Description
FastComparator()

Method Summary

Methods

Modifier and Type	Method and Description
abstract boolean	areEqual(T o1, T o2) Indicates if the specified objects can be considered equal.
abstract int	compare(T o1, T o2) Compares the specified objects for order.
abstract int	hashCodeOf(T obj) Returns the hash code for the specified object (consistent with areEqual(T, T)).

Methods inherited from class Object

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

Methods inherited from interface Comparator

equals

Field Detail

REHASH_SYSTEM_HASHCODE

public static final Configurable<Boolean> REHASH_SYSTEM_HASHCODE

Indicates if the system hash code should be rehashed (see Javolution Configuration for details).

DEFAULT

public static final FastComparator<Object> DEFAULT

Holds the default object comparator; rehash is performed if the system hash code (platform dependent) is not evenly distributed.

See Also:

Javolution Configuration

DIRECT

public static final FastComparator<Object> DIRECT

Holds the direct object comparator; no rehash is performed. Two objects o1 and o2 are considered equal if and only if o1.equals(o2). The compare(T, T) method throws ClassCastException if the specified objects are not Comparable.

REHASH

public static final FastComparator<Object> REHASH

Holds the comparator for objects with uneven hash distribution; objects hashcodes are rehashed. Two objects o1 and o2 are considered equal if and only if o1.equals(o2). The compare(T, T) method throws ClassCastException if the specified objects are not Comparable.

STRING

public static final FastComparator<String> STRING

Holds a fast comparator for java.lang.String. Hashcodes are calculated by taking a sample of few characters instead of the whole string.

IDENTITY

public static final FastComparator<Object> IDENTITY

Holds the identity comparator; poorly distributed system hashcodes are rehashed. Two objects o1 and o2 are considered equal if and only if (o1 == o2). The compare(T, T) method throws ClassCastException if the specified objects are not Comparable.

LEXICAL

public static final FastComparator<CharSequence> LEXICAL

Holds a lexicographic comparator for any CharSequence or String instances. Two objects are considered equal if and only if they represents the same character sequence). The hashcode is calculated using the following formula (same as for java.lang.String): s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]

Constructor Detail

FastComparator

public FastComparator()

Method Detail

hashCodeOf

public abstract int hashCodeOf(T obj)

Returns the hash code for the specified object (consistent with areEqual(T, T)). Two objects considered equal have the same hash code.

Parameters:

obj - the object to return the hashcode for.

Returns:

the hashcode for the specified object.

areEqual

public abstract boolean areEqual(T o1,
               T o2)

Indicates if the specified objects can be considered equal.

Parameters:

o1 - the first object (or null).

o2 - the second object (or null).

Returns:

true if both objects are considered equal; false otherwise.

compare

public abstract int compare(T o1,
          T o2)

Compares the specified objects for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.

Specified by:

compare in interface Comparator<T>

Parameters:

o1 - the first object.

o2 - the second object.

Returns:

a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.

Throws:

NullPointerException - if any of the specified object is null.