/*
* Copyright (c) 2000, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package javax.imageio.spi;
import java.util.AbstractSet;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;
/**
* A set of {@code Object}s with pairwise orderings between them.
* The {@code iterator} method provides the elements in
* topologically sorted order. Elements participating in a cycle
* are not returned.
*
* Unlike the {@code SortedSet} and {@code SortedMap}
* interfaces, which require their elements to implement the
* {@code Comparable} interface, this class receives ordering
* information via its {@code setOrdering} and
* {@code unsetPreference} methods. This difference is due to
* the fact that the relevant ordering between elements is unlikely to
* be inherent in the elements themselves; rather, it is set
* dynamically accoring to application policy. For example, in a
* service provider registry situation, an application might allow the
* user to set a preference order for service provider objects
* supplied by a trusted vendor over those supplied by another.
*
*/
class PartiallyOrderedSet<E> extends AbstractSet<E> {
// The topological sort (roughly) follows the algorithm described in
// Horowitz and Sahni, _Fundamentals of Data Structures_ (1976),
// p. 315.
// Maps Objects to DigraphNodes that contain them
private Map<E, DigraphNode<E>> poNodes = new HashMap<>();
// The set of Objects
private Set<E> nodes = poNodes.keySet();
/**
* Constructs a {@code PartiallyOrderedSet}.
*/
public PartiallyOrderedSet() {}
public int size() {
return nodes.size();
}
public boolean contains(Object o) {
return nodes.contains(o);
}
/**
* Returns an iterator over the elements contained in this
* collection, with an ordering that respects the orderings set
* by the {@code setOrdering} method.
*/
public Iterator<E> iterator() {
return new PartialOrderIterator<>(poNodes.values().iterator());
}
/**
* Adds an {@code Object} to this
* {@code PartiallyOrderedSet}.
*/
public boolean add(E o) {
if (nodes.contains(o)) {
return false;
}
DigraphNode<E> node = new DigraphNode<>(o);
poNodes.put(o, node);
return true;
}
/**
* Removes an {@code Object} from this
* {@code PartiallyOrderedSet}.
*/
public boolean remove(Object o) {
DigraphNode<E> node = poNodes.get(o);
if (node == null) {
return false;
}
poNodes.remove(o);
node.dispose();
return true;
}
public void clear() {
poNodes.clear();
}
/**
* Sets an ordering between two nodes. When an iterator is
* requested, the first node will appear earlier in the
* sequence than the second node. If a prior ordering existed
* between the nodes in the opposite order, it is removed.
*
* @return {@code true} if no prior ordering existed
* between the nodes, {@code false} otherwise.
*/
public boolean setOrdering(E first, E second) {
DigraphNode<E> firstPONode = poNodes.get(first);
DigraphNode<E> secondPONode = poNodes.get(second);
secondPONode.removeEdge(firstPONode);
return firstPONode.addEdge(secondPONode);
}
/**
* Removes any ordering between two nodes.
*
* @return true if a prior prefence existed between the nodes.
*/
public boolean unsetOrdering(E first, E second) {
DigraphNode<E> firstPONode = poNodes.get(first);
DigraphNode<E> secondPONode = poNodes.get(second);
return firstPONode.removeEdge(secondPONode) ||
secondPONode.removeEdge(firstPONode);
}
/**
* Returns {@code true} if an ordering exists between two
* nodes.
*/
public boolean hasOrdering(E preferred, E other) {
DigraphNode<E> preferredPONode = poNodes.get(preferred);
DigraphNode<E> otherPONode = poNodes.get(other);
return preferredPONode.hasEdge(otherPONode);
}
}
class PartialOrderIterator<E> implements Iterator<E> {
LinkedList<DigraphNode<E>> zeroList = new LinkedList<>();
Map<DigraphNode<E>, Integer> inDegrees = new HashMap<>();
public PartialOrderIterator(Iterator<DigraphNode<E>> iter) {
// Initialize scratch in-degree values, zero list
while (iter.hasNext()) {
DigraphNode<E> node = iter.next();
int inDegree = node.getInDegree();
inDegrees.put(node, inDegree);
// Add nodes with zero in-degree to the zero list
if (inDegree == 0) {
zeroList.add(node);
}
}
}
public boolean hasNext() {
return !zeroList.isEmpty();
}
public E next() {
DigraphNode<E> first = zeroList.removeFirst();
// For each out node of the output node, decrement its in-degree
Iterator<DigraphNode<E>> outNodes = first.getOutNodes();
while (outNodes.hasNext()) {
DigraphNode<E> node = outNodes.next();
int inDegree = inDegrees.get(node).intValue() - 1;
inDegrees.put(node, inDegree);
// If the in-degree has fallen to 0, place the node on the list
if (inDegree == 0) {
zeroList.add(node);
}
}
return first.getData();
}
public void remove() {
throw new UnsupportedOperationException();
}
}