120 lines
4.9 KiB
Java
120 lines
4.9 KiB
Java
/* Comparator.java -- Interface for objects that specify an ordering
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Copyright (C) 1998, 2001, 2004, 2005 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.util;
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/**
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* Interface for objects that specify an ordering between objects. The ordering
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* should be <em>total</em>, such that any two objects of the correct type
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* can be compared, and the comparison is reflexive, anti-symmetric, and
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* transitive. It is also recommended that the comparator be <em>consistent
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* with equals</em>, although this is not a strict requirement. A relation
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* is consistent with equals if these two statements always have the same
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* results (if no exceptions occur):<br>
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* <code>compare((Object) e1, (Object) e2) == 0</code> and
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* <code>e1.equals((Object) e2)</code><br>
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* Comparators that violate consistency with equals may cause strange behavior
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* in sorted lists and sets. For example, a case-sensitive dictionary order
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* comparison of Strings is consistent with equals, but if it is
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* case-insensitive it is not, because "abc" and "ABC" compare as equal even
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* though "abc".equals("ABC") returns false.
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* <P>
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* In general, Comparators should be Serializable, because when they are passed
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* to Serializable data structures such as SortedMap or SortedSet, the entire
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* data structure will only serialize correctly if the comparator is
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* Serializable.
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*
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* @author Original author unknown
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* @author Eric Blake (ebb9@email.byu.edu)
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* @see Comparable
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* @see TreeMap
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* @see TreeSet
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* @see SortedMap
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* @see SortedSet
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* @see Arrays#sort(Object[], Comparator)
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* @see java.io.Serializable
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* @since 1.2
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* @status updated to 1.4
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*/
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public interface Comparator<T>
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{
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/**
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* Return an integer that is negative, zero or positive depending on whether
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* the first argument is less than, equal to or greater than the second
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* according to this ordering. This method should obey the following
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* contract:
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* <ul>
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* <li>if compare(a, b) < 0 then compare(b, a) > 0</li>
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* <li>if compare(a, b) throws an exception, so does compare(b, a)</li>
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* <li>if compare(a, b) < 0 and compare(b, c) < 0 then compare(a, c)
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* < 0</li>
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* <li>if compare(a, b) == 0 then compare(a, c) and compare(b, c) must
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* have the same sign</li>
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* </ul>
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* To be consistent with equals, the following additional constraint is
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* in place:
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* <ul>
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* <li>if a.equals(b) or both a and b are null, then
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* compare(a, b) == 0.</li>
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* </ul><p>
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*
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* Although it is permissible for a comparator to provide an order
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* inconsistent with equals, that should be documented.
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*
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* @param o1 the first object
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* @param o2 the second object
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* @return the comparison
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* @throws ClassCastException if the elements are not of types that can be
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* compared by this ordering.
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*/
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int compare(T o1, T o2);
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/**
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* Return true if the object is equal to this object. To be
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* considered equal, the argument object must satisfy the constraints
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* of <code>Object.equals()</code>, be a Comparator, and impose the
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* same ordering as this Comparator. The default implementation
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* inherited from Object is usually adequate.
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*
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* @param obj The object
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* @return true if it is a Comparator that imposes the same order
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* @see Object#equals(Object)
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*/
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boolean equals(Object obj);
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}
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