1 /*
2 * Copyright 2000 Sun Microsystems, Inc. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25
26 package javax.imageio.spi;
27
28 import java.util.AbstractSet;
29 import java.util.HashMap;
30 import java.util.Iterator;
31 import java.util.LinkedList;
32 import java.util.Map;
33 import java.util.Set;
34
35 /**
36 * A set of <code>Object</code>s with pairwise orderings between them.
37 * The <code>iterator</code> method provides the elements in
38 * topologically sorted order. Elements participating in a cycle
39 * are not returned.
40 *
41 * Unlike the <code>SortedSet</code> and <code>SortedMap</code>
42 * interfaces, which require their elements to implement the
43 * <code>Comparable</code> interface, this class receives ordering
44 * information via its <code>setOrdering</code> and
45 * <code>unsetPreference</code> methods. This difference is due to
46 * the fact that the relevant ordering between elements is unlikely to
47 * be inherent in the elements themselves; rather, it is set
48 * dynamically accoring to application policy. For example, in a
49 * service provider registry situation, an application might allow the
50 * user to set a preference order for service provider objects
51 * supplied by a trusted vendor over those supplied by another.
52 *
53 */
54 class PartiallyOrderedSet extends AbstractSet {
55
56 // The topological sort (roughly) follows the algorithm described in
57 // Horowitz and Sahni, _Fundamentals of Data Structures_ (1976),
58 // p. 315.
59
60 // Maps Objects to DigraphNodes that contain them
61 private Map poNodes = new HashMap();
62
63 // The set of Objects
64 private Set nodes = poNodes.keySet();
65
66 /**
67 * Constructs a <code>PartiallyOrderedSet</code>.
68 */
69 public PartiallyOrderedSet() {}
70
71 public int size() {
72 return nodes.size();
73 }
74
75 public boolean contains(Object o) {
76 return nodes.contains(o);
77 }
78
79 /**
80 * Returns an iterator over the elements contained in this
81 * collection, with an ordering that respects the orderings set
82 * by the <code>setOrdering</code> method.
83 */
84 public Iterator iterator() {
85 return new PartialOrderIterator(poNodes.values().iterator());
86 }
87
88 /**
89 * Adds an <code>Object</code> to this
90 * <code>PartiallyOrderedSet</code>.
91 */
92 public boolean add(Object o) {
93 if (nodes.contains(o)) {
94 return false;
95 }
96
97 DigraphNode node = new DigraphNode(o);
98 poNodes.put(o, node);
99 return true;
100 }
101
102 /**
103 * Removes an <code>Object</code> from this
104 * <code>PartiallyOrderedSet</code>.
105 */
106 public boolean remove(Object o) {
107 DigraphNode node = (DigraphNode)poNodes.get(o);
108 if (node == null) {
109 return false;
110 }
111
112 poNodes.remove(o);
113 node.dispose();
114 return true;
115 }
116
117 public void clear() {
118 poNodes.clear();
119 }
120
121 /**
122 * Sets an ordering between two nodes. When an iterator is
123 * requested, the first node will appear earlier in the
124 * sequence than the second node. If a prior ordering existed
125 * between the nodes in the opposite order, it is removed.
126 *
127 * @return <code>true</code> if no prior ordering existed
128 * between the nodes, <code>false</code>otherwise.
129 */
130 public boolean setOrdering(Object first, Object second) {
131 DigraphNode firstPONode =
132 (DigraphNode)poNodes.get(first);
133 DigraphNode secondPONode =
134 (DigraphNode)poNodes.get(second);
135
136 secondPONode.removeEdge(firstPONode);
137 return firstPONode.addEdge(secondPONode);
138 }
139
140 /**
141 * Removes any ordering between two nodes.
142 *
143 * @return true if a prior prefence existed between the nodes.
144 */
145 public boolean unsetOrdering(Object first, Object second) {
146 DigraphNode firstPONode =
147 (DigraphNode)poNodes.get(first);
148 DigraphNode secondPONode =
149 (DigraphNode)poNodes.get(second);
150
151 return firstPONode.removeEdge(secondPONode) ||
152 secondPONode.removeEdge(firstPONode);
153 }
154
155 /**
156 * Returns <code>true</code> if an ordering exists between two
157 * nodes.
158 */
159 public boolean hasOrdering(Object preferred, Object other) {
160 DigraphNode preferredPONode =
161 (DigraphNode)poNodes.get(preferred);
162 DigraphNode otherPONode =
163 (DigraphNode)poNodes.get(other);
164
165 return preferredPONode.hasEdge(otherPONode);
166 }
167 }
168
169 class PartialOrderIterator implements Iterator {
170
171 LinkedList zeroList = new LinkedList();
172 Map inDegrees = new HashMap(); // DigraphNode -> Integer
173
174 public PartialOrderIterator(Iterator iter) {
175 // Initialize scratch in-degree values, zero list
176 while (iter.hasNext()) {
177 DigraphNode node = (DigraphNode)iter.next();
178 int inDegree = node.getInDegree();
179 inDegrees.put(node, new Integer(inDegree));
180
181 // Add nodes with zero in-degree to the zero list
182 if (inDegree == 0) {
183 zeroList.add(node);
184 }
185 }
186 }
187
188 public boolean hasNext() {
189 return !zeroList.isEmpty();
190 }
191
192 public Object next() {
193 DigraphNode first = (DigraphNode)zeroList.removeFirst();
194
195 // For each out node of the output node, decrement its in-degree
196 Iterator outNodes = first.getOutNodes();
197 while (outNodes.hasNext()) {
198 DigraphNode node = (DigraphNode)outNodes.next();
199 int inDegree = ((Integer)inDegrees.get(node)).intValue() - 1;
200 inDegrees.put(node, new Integer(inDegree));
201
202 // If the in-degree has fallen to 0, place the node on the list
203 if (inDegree == 0) {
204 zeroList.add(node);
205 }
206 }
207
208 return first.getData();
209 }
210
211 public void remove() {
212 throw new UnsupportedOperationException();
213 }
214 }
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