1  // HTMLParser Library $Name: v1_6_20060319 $ - A java-based parser for HTML
 2  // http://sourceforge.org/projects/htmlparser
 3  // Copyright (C) 2004 Derrick Oswald
 4  //
 5  // Revision Control Information
 6  //
 7  // $Source: /cvsroot/htmlparser/htmlparser/src/org/htmlparser/util/sort/Ordered.java,v $
 8  // $Author: derrickoswald $
 9  // $Date: 2004/01/02 16:24:58 $
10  // $Revision: 1.11 $
11  //
12  // This library is free software; you can redistribute it and/or
13  // modify it under the terms of the GNU Lesser General Public
14  // License as published by the Free Software Foundation; either
15  // version 2.1 of the License, or (at your option) any later version.
16  //
17  // This library is distributed in the hope that it will be useful,
18  // but WITHOUT ANY WARRANTY; without even the implied warranty of
19  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
20  // Lesser General Public License for more details.
21  //
22  // You should have received a copy of the GNU Lesser General Public
23  // License along with this library; if not, write to the Free Software
24  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
25  //
26  
27  package org.htmlparser.util.sort;
28  
29  /**
30   * Describes an object that knows about ordering.
31   * Implementors must have a comparison function,
32   * which imposes a partial ordering on some
33   * collection of objects. Ordered objects can be passed to a
34   * sort method (such as org.htmlparser.util.sort.Sort) to allow precise control
35   * over the sort order.
36   * <p>
37   * An set of elements S is partially ordered
38   * if and only if <code>e1.compare(e2)==0</code> implies that
39   * <code>e1.equals(e2)</code> for every e1 and e2 in S.
40   * <p>
41   * This all goes away in JDK 1.2.
42   * <p>
43   * For use with java.lang.Comparable from JDK 1.2:
44   * <pre>
45   * public int compare (Object o1, Object o2)
46   * {
47   *     return (((Ordered)o1).compare (o2));
48   * }
49   * </pre>
50   * @see Sort
51   */
52  public interface Ordered
53  {
54      /**
55       * Compares this object with another for order.
56       * Returns a negative integer, zero, or a positive integer
57       * as this object is less than, equal to, or greater
58       * than the second.
59       * <p>
60       * The implementor must ensure that
61       * <code>sgn(x.compare(y)) == -sgn(y.compare(x))</code>
62       * for all x and y. (This implies that <code>x.compare(y)</code>
63       * must throw an exception if and only if <code>y.compare(x)</code>
64       * throws an exception.)
65       * <p>
66       * The implementor must also ensure that the relation is transitive:
67       * <code>((x.compare(y)>0) && (y.compare(z)>0))</code>
68       * implies <code>x.compare(z)>0</code>.
69       * <p>
70       * Finally, the implementer must ensure that
71       * <code>x.compare(y)==0</code> implies that
72       * <code>sgn(x.compare(z))==sgn(y.compare(z))</code>
73       * for all z.
74       * @param that The object to compare this object against.
75       * @return A negative integer, zero, or a positive
76       * integer as this object is less than, equal to,
77       * or greater than the second.
78       * @exception ClassCastException The arguments type prevents it
79       * from being compared by this Ordered.
80       */
81      public int compare (Object that);
82  }