1 /*
2 * org.riverock.dbrevision - Database revision engine
3 * For more information about DbRevision, please visit project site
4 * http://www.riverock.org
5 *
6 * Copyright (C) 2006-2006, Riverock Software, All Rights Reserved.
7 *
8 * Riverock - The Open-source Java Development Community
9 * http://www.riverock.org
10 *
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 package org.riverock.dbrevision.db;
27
28 import java.util.Comparator;
29 import java.io.Serializable;
30
31 import org.riverock.dbrevision.annotation.schema.db.DbPrimaryKeyColumn;
32
33 /**
34 * @author Sergei Maslyukov
35 * Date: 28.11.2006
36 * Time: 17:31:51
37 * <p/>
38 * $Id$
39 */
40 public class DbPkComparator implements Comparator<DbPrimaryKeyColumn>, Serializable {
41 private final static DbPkComparator DB_PK_COMPARATOR = new DbPkComparator();
42
43 public static DbPkComparator getInstance() {
44 return DB_PK_COMPARATOR;
45 }
46
47 /**
48 * Compares its two arguments for order. Returns a negative integer,
49 * zero, or a positive integer as the first argument is less than, equal
50 * to, or greater than the second.<p>
51 * <p/>
52 * The implementor must ensure that <tt>sgn(compare(x, y)) ==
53 * -sgn(compare(y, x))</tt> for all <tt>x</tt> and <tt>y</tt>. (This
54 * implies that <tt>compare(x, y)</tt> must throw an exception if and only
55 * if <tt>compare(y, x)</tt> throws an exception.)<p>
56 * <p/>
57 * The implementor must also ensure that the relation is transitive:
58 * <tt>((compare(x, y)>0) && (compare(y, z)>0))</tt> implies
59 * <tt>compare(x, z)>0</tt>.<p>
60 * <p/>
61 * Finally, the implementer must ensure that <tt>compare(x, y)==0</tt>
62 * implies that <tt>sgn(compare(x, z))==sgn(compare(y, z))</tt> for all
63 * <tt>z</tt>.<p>
64 * <p/>
65 * It is generally the case, but <i>not</i> strictly required that
66 * <tt>(compare(x, y)==0) == (x.equals(y))</tt>. Generally speaking,
67 * any comparator that violates this condition should clearly indicate
68 * this fact. The recommended language is "Note: this comparator
69 * imposes orderings that are inconsistent with equals."
70 *
71 * @param o1 the first object to be compared.
72 * @param o2 the second object to be compared.
73 * @return a negative integer, zero, or a positive integer as the
74 * first argument is less than, equal to, or greater than the
75 * second.
76 * @throws ClassCastException if the arguments' types prevent them from
77 * being compared by this Comparator.
78 */
79 public int compare(DbPrimaryKeyColumn o1, DbPrimaryKeyColumn o2) {
80 if (o1.getKeySeq()<o2.getKeySeq()) {
81 return -1;
82 }
83 else if (o1.getKeySeq()==o2.getKeySeq()) {
84 return 0;
85 }
86 return 1;
87 }
88 }