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From-SVN: r102074

libjava/classpath/java/lang/Comparable.java

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+/* Comparable.java -- Interface for comparaing objects to obtain an ordering
+   Copyright (C) 1998, 1999, 2001, 2002, 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.lang;
+
+/**
+ * Interface for objects that can be ordering among other objects. The
+ * ordering can be <em>total</em>, such that two objects only compare equal
+ * if they are also equal by the equals method, or <em>partial</em> such
+ * that this is not necessarily true. For example, a case-sensitive
+ * dictionary order comparison of Strings is total, but if it is
+ * case-insensitive it is partial, because "abc" and "ABC" compare as
+ * equal even though "abc".equals("ABC") returns false. However, if you use
+ * a partial ordering, it is a good idea to document your class as
+ * "inconsistent with equals", because the behavior of your class in a
+ * SortedMap will be different than in a HashMap.
+ *
+ * <p>Lists, arrays, and sets of objects that implement this interface can
+ * be sorted automatically, without the need for an explicit
+ * {@link java.util.Comparator}. Note that <code>e1.compareTo(null)</code> 
+ * should throw an Exception; as should comparison between incompatible 
+ * classes.
+ *
+ * @author Geoff Berry
+ * @author Warren Levy (warrenl@cygnus.com)
+ * @see java.util.Comparator
+ * @see java.util.Collections#sort(java.util.List)
+ * @see java.util.Arrays#sort(Object[])
+ * @see java.util.SortedSet
+ * @see java.util.SortedMap
+ * @see java.util.TreeSet
+ * @see java.util.TreeMap
+ * @since 1.2
+ * @status updated to 1.4
+ */
+public interface Comparable
+{
+  /**
+   * Compares this object with another, and returns a numerical result based
+   * on the comparison.  If the result is negative, this object sorts less
+   * than the other; if 0, the two are equal, and if positive, this object
+   * sorts greater than the other.  To translate this into boolean, simply
+   * perform <code>o1.compareTo(o2) <em>&lt;op&gt;</em> 0</code>, where op
+   * is one of &lt;, &lt;=, =, !=, &gt;, or &gt;=.
+   *
+   * <p>You must make sure that the comparison is mutual, ie.
+   * <code>sgn(x.compareTo(y)) == -sgn(y.compareTo(x))</code> (where sgn() is
+   * defined as -1, 0, or 1 based on the sign).  This includes throwing an
+   * exception in either direction if the two are not comparable; hence,
+   * <code>compareTo(null)</code> should always throw an Exception.
+   *
+   * <p>You should also ensure transitivity, in two forms:
+   * <code>x.compareTo(y) &gt; 0 && y.compareTo(z) &gt; 0</code> implies
+   * <code>x.compareTo(z) &gt; 0</code>; and <code>x.compareTo(y) == 0</code>
+   * implies <code>x.compareTo(z) == y.compareTo(z)</code>.
+   *
+   * @param o the object to be compared
+   * @return an integer describing the comparison
+   * @throws NullPointerException if o is null
+   * @throws ClassCastException if o cannot be compared
+   */
+  int compareTo(Object o);
+}