FastComparator - JBoss RULES 3.0.6 API 英文版文档

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org.drools.util
Class FastComparator

java.lang.Object
  org.drools.util.FastComparator

All Implemented Interfaces:: java.io.Serializable, java.util.Comparator

Direct Known Subclasses:: EqualityAssertMapComparator, EqualityKeyComparator, IdentityAssertMapComparator

public abstract class FastComparator
extends java.lang.Object
implements java.util.Comparator, java.io.Serializable
extends java.lang.Object
implements java.util.Comparator, java.io.Serializable

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.

See Also:: Serialized Form

Field Summary

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

static FastComparator DIRECT
          Holds the direct object comparator; no rehash is performed.

static FastComparator IDENTITY
          Holds the identity comparator; poorly distributed system hashcodes are rehashed.

static FastComparator LEXICAL
          Holds a lexicographic comparator for any CharSequence or String instances.

static FastComparator REHASH
          Holds the comparator for objects with uneven hash distribution; objects hashcodes are rehashed.

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

Constructor Summary

FastComparator()


Method Summary

abstract boolean areEqual(java.lang.Object o1, java.lang.Object o2)
          Indicates if the specified objects can be considered equal.

abstract int compare(java.lang.Object o1, java.lang.Object o2)
          Compares the specified objects for order.

abstract int hashCodeOf(java.lang.Object obj)
          Returns the hash code for the specified object (consistent with areEqual(java.lang.Object, java.lang.Object)).

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

Field Summary
`static FastComparator`	`DEFAULT` Holds the default object comparator; rehash is performed if the system hash code (platform dependent) is not evenly distributed.
`static FastComparator`	`DIRECT` Holds the direct object comparator; no rehash is performed.
`static FastComparator`	`IDENTITY` Holds the identity comparator; poorly distributed system hashcodes are rehashed.
`static FastComparator`	`LEXICAL` Holds a lexicographic comparator for any `CharSequence` or `String` instances.
`static FastComparator`	`REHASH` Holds the comparator for objects with uneven hash distribution; objects hashcodes are rehashed.
`static boolean`	`REHASH_SYSTEM_HASHCODE` Indicates if the system hash code should be rehashed (see Javolution Configuration for details).

Constructor Summary
`FastComparator()`

Method Summary
`abstract boolean`	`areEqual(java.lang.Object o1, java.lang.Object o2)` Indicates if the specified objects can be considered equal.
`abstract int`	`compare(java.lang.Object o1, java.lang.Object o2)` Compares the specified objects for order.
`abstract int`	`hashCodeOf(java.lang.Object obj)` Returns the hash code for the specified object (consistent with `areEqual(java.lang.Object, java.lang.Object)`).

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`

Field Detail

REHASH_SYSTEM_HASHCODE

public static final boolean REHASH_SYSTEM_HASHCODE

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

DEFAULT

public static final FastComparator 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 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(java.lang.Object, java.lang.Object) method throws ClassCastException if the specified objects are not Comparable.

REHASH

public static final FastComparator 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(java.lang.Object, java.lang.Object) method throws ClassCastException if the specified objects are not Comparable.

IDENTITY

public static final FastComparator 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(java.lang.Object, java.lang.Object) method throws ClassCastException if the specified objects are not Comparable.

LEXICAL

public static final FastComparator 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(java.lang.Object obj)

Returns the hash code for the specified object (consistent with areEqual(java.lang.Object, java.lang.Object)). 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.
Throws:: java.lang.NullPointerException - if the specified object is null.

areEqual

public abstract boolean areEqual(java.lang.Object o1,
                                 java.lang.Object 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(java.lang.Object o1,
                            java.lang.Object 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 java.util.Comparator

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:: java.lang.NullPointerException - if any of the specified object is null.