| /* Comparator.java -- Interface for objects that specify an ordering |
| Copyright (C) 1998, 2001, 2005 Free Software Foundation, Inc. |
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| This file is part of GNU Classpath. |
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| |
| |
| 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); |
| } |