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Diffstat (limited to 'libjava/classpath/java/util/Comparator.java')
| -rw-r--r-- | libjava/classpath/java/util/Comparator.java | 119 |
1 files changed, 119 insertions, 0 deletions
diff --git a/libjava/classpath/java/util/Comparator.java b/libjava/classpath/java/util/Comparator.java new file mode 100644 index 00000000000..386bdc1d6a2 --- /dev/null +++ b/libjava/classpath/java/util/Comparator.java @@ -0,0 +1,119 @@ +/* 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) < 0 then compare(b, a) > 0</li> + * <li>if compare(a, b) throws an exception, so does compare(b, a)</li> + * <li>if compare(a, b) < 0 and compare(b, c) < 0 then compare(a, c) + * < 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); +} |