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/*
* Javolution - Java(TM) Solution for Real-Time and Embedded Systems
* Copyright (C) 2012 - Javolution (http://javolution.org/)
* All rights reserved.
*
* Permission to use, copy, modify, and distribute this software is
* freely granted, provided that this notice is preserved.
*/
package javolution.util.function;
import java.util.Comparator;
/**
* A comparator to be used for element equality as well as for
* ordering. Implementing classes should ensure that:
*
* - The {@link #compare compare} function is consistent with
* {@link #areEqual equals}. If two objects {@link #compare compare}
* to {@code 0} then they are {@link #areEqual equals} and the
* the reciprocal is true (this ensures that sorted collections/maps
* do not break the general contract of their parent class based on
* object equal).
* - The {@link #hashCodeOf hashcode} function is consistent with
* {@link #areEqual equals}: If two objects are equals, they have
* the same hashcode (the reciprocal is not true).
* - The {@code null} value is supported (even for
* {@link #compare comparisons}) and the {@link #hashCodeOf(Object)
* hashcode} value of {@code null} is {@code 0}.
*
*
*
* @param the type of objects that may be compared for equality or order.
*
* @author Jean-Marie Dautelle
* @version 6.0, July 21, 2013
* @see Equalities
*/
public interface Equality extends Comparator {
/**
* Returns the hash code for the specified object (consistent with
* {@link #areEqual}). Two objects considered {@link #areEqual equal} have
* the same hash code. The hash code of null is always
* 0.
*
* @param object the object to return the hashcode for.
* @return the hashcode for the specified object.
*/
int hashCodeOf(T object);
/**
* Indicates if the specified objects can be considered equal.
* This methods is equivalent to {@code (compare(o1, o2) == 0)} but
* usually faster.
*
* @param left the first object (or null).
* @param right the second object (or null).
* @return true if both objects are considered equal;
* false otherwise.
*/
boolean areEqual(T left, T right);
/**
* Compares the specified objects for order. Returns a negative integer,
* zero, or a positive integer as the first argument is less than, possibly
* equal to, or greater than the second. Implementation classes should
* ensure that comparisons with {@code null} is supported.
*
* @param left the first object.
* @param right the second object.
* @return a negative integer, zero, or a positive integer as the first
* argument is less than, possibly equal to, or greater than the second.
*/
int compare(T left, T right);
}