1 /*
2 * Copyright (c) 2000, Oracle and/or its affiliates. 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. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * 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<E> extends AbstractSet<E> {
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<E, DigraphNode<E>> poNodes = new HashMap<>();
62
63 // The set of Objects
64 private Set<E> 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<E> 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(E o) {
93 if (nodes.contains(o)) {
94 return false;
95 }
96
97 DigraphNode<E> 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<E> node = 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(E first, E second) {
131 DigraphNode<E> firstPONode = poNodes.get(first);
132 DigraphNode<E> secondPONode = poNodes.get(second);
133
134 secondPONode.removeEdge(firstPONode);
135 return firstPONode.addEdge(secondPONode);
136 }
137
138 /**
139 * Removes any ordering between two nodes.
140 *
141 * @return true if a prior prefence existed between the nodes.
142 */
143 public boolean unsetOrdering(E first, E second) {
144 DigraphNode<E> firstPONode = poNodes.get(first);
145 DigraphNode<E> secondPONode = poNodes.get(second);
146
147 return firstPONode.removeEdge(secondPONode) ||
148 secondPONode.removeEdge(firstPONode);
149 }
150
151 /**
152 * Returns <code>true</code> if an ordering exists between two
153 * nodes.
154 */
155 public boolean hasOrdering(E preferred, E other) {
156 DigraphNode<E> preferredPONode = poNodes.get(preferred);
157 DigraphNode<E> otherPONode = poNodes.get(other);
158
159 return preferredPONode.hasEdge(otherPONode);
160 }
161 }
162
163 class PartialOrderIterator<E> implements Iterator<E> {
164
165 LinkedList<DigraphNode<E>> zeroList = new LinkedList<>();
166 Map<DigraphNode<E>, Integer> inDegrees = new HashMap<>();
167
168 public PartialOrderIterator(Iterator<DigraphNode<E>> iter) {
169 // Initialize scratch in-degree values, zero list
170 while (iter.hasNext()) {
171 DigraphNode<E> node = iter.next();
172 int inDegree = node.getInDegree();
173 inDegrees.put(node, new Integer(inDegree));
174
175 // Add nodes with zero in-degree to the zero list
176 if (inDegree == 0) {
177 zeroList.add(node);
178 }
179 }
180 }
181
182 public boolean hasNext() {
183 return !zeroList.isEmpty();
184 }
185
186 public E next() {
187 DigraphNode<E> first = zeroList.removeFirst();
188
189 // For each out node of the output node, decrement its in-degree
190 Iterator<DigraphNode<E>> outNodes = first.getOutNodes();
191 while (outNodes.hasNext()) {
192 DigraphNode<E> node = outNodes.next();
193 int inDegree = inDegrees.get(node).intValue() - 1;
194 inDegrees.put(node, new Integer(inDegree));
195
196 // If the in-degree has fallen to 0, place the node on the list
197 if (inDegree == 0) {
198 zeroList.add(node);
199 }
200 }
201
202 return first.getData();
203 }
204
205 public void remove() {
206 throw new UnsupportedOperationException();
207 }
208 }