| /* |
| * Copyright (c) 1997, 2012, 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 |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| package com.sun.tools.internal.xjc.reader.gbind; |
| |
| import java.util.ArrayList; |
| import java.util.Collections; |
| import java.util.Iterator; |
| import java.util.LinkedHashSet; |
| import java.util.List; |
| import java.util.Set; |
| |
| /** |
| * {@link Expression} that represents an alphabet of a regular language. |
| * |
| * <p> |
| * Since this package is about a regular expression over element declarations, |
| * this represents an XML element declaration (hence the name.) |
| * |
| * Element needs to be interned, meaning one {@link Element} per one tag name. |
| * |
| * <p> |
| * Implements {@link ElementSet} to represent a self. |
| * |
| * @author Kohsuke Kawaguchi |
| */ |
| public abstract class Element extends Expression implements ElementSet { |
| /** |
| * Once we build a graph from {@link Expression}, |
| * we represent an edge e1 -> e2 by {@code e1.foreEdges.contains(e2)} |
| * and {@code e2.backEdges.contains(e1)}. |
| */ |
| final Set<Element> foreEdges = new LinkedHashSet<Element>(); |
| final Set<Element> backEdges = new LinkedHashSet<Element>(); |
| |
| /** |
| * Previous element in the DFS post-order traveral |
| * of the element graph. |
| * |
| * <p> |
| * We use {@code prevPostOrder==null} as a check if the element is visted in DFS, |
| * so this chain terminates by a self-reference, not by having null. |
| * |
| * Set in {@link #assignDfsPostOrder(Element)} |
| */ |
| /*package*/ Element prevPostOrder; |
| |
| /** |
| * {@link ConnectedComponent} to which this element belongs. |
| * |
| * Set in {@link #buildStronglyConnectedComponents(List<ConnectedComponent>)} |
| */ |
| private ConnectedComponent cc; |
| |
| protected Element() { |
| } |
| |
| ElementSet lastSet() { |
| return this; |
| } |
| |
| boolean isNullable() { |
| return false; |
| } |
| |
| /** |
| * True if this {@link Element} is {@link SourceNode}. |
| */ |
| boolean isSource() { |
| return false; |
| } |
| |
| /** |
| * True if this {@link Element} is {@link SinkNode}. |
| */ |
| boolean isSink() { |
| return false; |
| } |
| |
| void buildDAG(ElementSet incoming) { |
| incoming.addNext(this); |
| } |
| |
| public void addNext(Element element) { |
| foreEdges.add(element); |
| element.backEdges.add(this); |
| } |
| |
| public boolean contains(ElementSet rhs) { |
| return this==rhs || rhs==ElementSet.EMPTY_SET; |
| } |
| |
| /** |
| * Just to satisfy the {@link ElementSet} contract. |
| * |
| * @deprecated |
| * if you statically call this method, there's something wrong. |
| */ |
| public Iterator<Element> iterator() { |
| return Collections.singleton(this).iterator(); |
| } |
| |
| /** |
| * Traverses the {@link Element} graph with DFS |
| * and set {@link #prevPostOrder}. |
| * |
| * Should be first invoked on the source node of the graph. |
| */ |
| /*package*/ Element assignDfsPostOrder(Element prev) { |
| if(prevPostOrder!=null) |
| return prev; // already visited |
| |
| prevPostOrder = this; // set a dummy value to prepare for cycles |
| |
| for (Element next : foreEdges) { |
| prev = next.assignDfsPostOrder(prev); |
| } |
| this.prevPostOrder = prev; // set to the real value |
| return this; |
| } |
| |
| /** |
| * Builds a set of strongly connected components and puts them |
| * all into the given set. |
| */ |
| public void buildStronglyConnectedComponents(List<ConnectedComponent> ccs) { |
| |
| // store visited elements - loop detection |
| List<Element> visitedElements = new ArrayList<Element>(); |
| |
| for(Element cur=this; cur!=cur.prevPostOrder; cur=cur.prevPostOrder) { |
| |
| if(visitedElements.contains(cur)) { |
| // if I've already processed cur element, I'm in a loop |
| break; |
| } else { |
| visitedElements.add(cur); |
| } |
| |
| if(cur.belongsToSCC()) |
| continue; |
| |
| // start a new component |
| ConnectedComponent cc = new ConnectedComponent(); |
| ccs.add(cc); |
| |
| cur.formConnectedComponent(cc); |
| } |
| } |
| |
| private boolean belongsToSCC() { |
| return cc!=null || isSource() || isSink(); |
| } |
| |
| /** |
| * Forms a strongly connected component by doing a reverse DFS. |
| */ |
| private void formConnectedComponent(ConnectedComponent group) { |
| if(belongsToSCC()) |
| return; |
| |
| this.cc=group; |
| group.add(this); |
| for (Element prev : backEdges) |
| prev.formConnectedComponent(group); |
| } |
| |
| public boolean hasSelfLoop() { |
| // if foreEdges have a loop, backEdges must have one. Or vice versa |
| assert foreEdges.contains(this)==backEdges.contains(this); |
| |
| return foreEdges.contains(this); |
| } |
| |
| /** |
| * Checks if the given {@link ConnectedComponent} forms a cut-set |
| * of a graph. |
| * |
| * @param visited |
| * Used to keep track of visited nodes. |
| * @return |
| * true if it is indeed a cut-set. false if not. |
| */ |
| /*package*/ final boolean checkCutSet(ConnectedComponent cc, Set<Element> visited) { |
| assert belongsToSCC(); // SCC discomposition must be done first |
| |
| if(isSink()) |
| // the definition of the cut set is that without those nodes |
| // you can't reach from soruce to sink |
| return false; |
| |
| if(!visited.add(this)) |
| return true; |
| |
| if(this.cc==cc) |
| return true; |
| |
| for (Element next : foreEdges) { |
| if(!next.checkCutSet(cc,visited)) |
| // we've found a path to the sink |
| return false; |
| } |
| |
| return true; |
| } |
| } |