Source for java.lang.Comparable

   1: /* Comparable.java -- Interface for comparaing objects to obtain an ordering
   2:    Copyright (C) 1998, 1999, 2001, 2002, 2004, 2005 Free Software Foundation, Inc.
   3: 
   4: This file is part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2, or (at your option)
   9: any later version.
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  11: GNU Classpath is distributed in the hope that it will be useful, but
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  14: General Public License for more details.
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  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; see the file COPYING.  If not, write to the
  18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 USA.
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  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
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  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
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  31: independent module, the terms and conditions of the license of that
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  36: exception statement from your version. */
  37: 
  38: 
  39: package java.lang;
  40: 
  41: /**
  42:  * Interface for objects that can be ordering among other objects. The
  43:  * ordering can be <em>total</em>, such that two objects only compare equal
  44:  * if they are also equal by the equals method, or <em>partial</em> such
  45:  * that this is not necessarily true. For example, a case-sensitive
  46:  * dictionary order comparison of Strings is total, but if it is
  47:  * case-insensitive it is partial, because "abc" and "ABC" compare as
  48:  * equal even though "abc".equals("ABC") returns false. However, if you use
  49:  * a partial ordering, it is a good idea to document your class as
  50:  * "inconsistent with equals", because the behavior of your class in a
  51:  * SortedMap will be different than in a HashMap.
  52:  *
  53:  * <p>Lists, arrays, and sets of objects that implement this interface can
  54:  * be sorted automatically, without the need for an explicit
  55:  * {@link java.util.Comparator}. Note that <code>e1.compareTo(null)</code> 
  56:  * should throw an Exception; as should comparison between incompatible 
  57:  * classes.
  58:  *
  59:  * @author Geoff Berry
  60:  * @author Warren Levy (warrenl@cygnus.com)
  61:  * @see java.util.Comparator
  62:  * @see java.util.Collections#sort(java.util.List)
  63:  * @see java.util.Arrays#sort(Object[])
  64:  * @see java.util.SortedSet
  65:  * @see java.util.SortedMap
  66:  * @see java.util.TreeSet
  67:  * @see java.util.TreeMap
  68:  * @since 1.2
  69:  * @status updated to 1.5
  70:  */
  71: public interface Comparable<T>
  72: {
  73:   /**
  74:    * Compares this object with another, and returns a numerical result based
  75:    * on the comparison.  If the result is negative, this object sorts less
  76:    * than the other; if 0, the two are equal, and if positive, this object
  77:    * sorts greater than the other.  To translate this into boolean, simply
  78:    * perform <code>o1.compareTo(o2) <em>&lt;op&gt;</em> 0</code>, where op
  79:    * is one of &lt;, &lt;=, =, !=, &gt;, or &gt;=.
  80:    *
  81:    * <p>You must make sure that the comparison is mutual, ie.
  82:    * <code>sgn(x.compareTo(y)) == -sgn(y.compareTo(x))</code> (where sgn() is
  83:    * defined as -1, 0, or 1 based on the sign).  This includes throwing an
  84:    * exception in either direction if the two are not comparable; hence,
  85:    * <code>compareTo(null)</code> should always throw an Exception.
  86:    *
  87:    * <p>You should also ensure transitivity, in two forms:
  88:    * <code>x.compareTo(y) &gt; 0 && y.compareTo(z) &gt; 0</code> implies
  89:    * <code>x.compareTo(z) &gt; 0</code>; and <code>x.compareTo(y) == 0</code>
  90:    * implies <code>x.compareTo(z) == y.compareTo(z)</code>.
  91:    *
  92:    * @param o the object to be compared
  93:    * @return an integer describing the comparison
  94:    * @throws NullPointerException if o is null
  95:    * @throws ClassCastException if o cannot be compared
  96:    */
  97:   int compareTo(T o);
  98: }