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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.

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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 <, <=, =, !=, >, or >=.

   *

   * <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);

}