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From-SVN: r102074

libjava/classpath/java/util/Comparator.java

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