Mercurial > jdk8-mips64-public > langtools / file revision

 /*

  * Copyright (c) 1999, 2013, 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.javac.util;

 /** <p><b>This is NOT part of any supported API.

  *  If you write code that depends on this, you do so at your own risk.

  *  This code and its internal interfaces are subject to change or

  *  deletion without notice.</b>

  */

 public class GraphUtils {

     /**

      * This class is a basic abstract class for representing a node.

      * A node is associated with a given data.

      */

     public static abstract class Node<D> {

         public final D data;

         public Node(D data) {

             this.data = data;

         }

         public abstract Iterable<? extends Node<D>> getDependencies();

         public abstract String printDependency(Node<D> to);

         @Override

         public String toString() {

             return data.toString();

         }

     }

     /**

      * This class specialized Node, by adding elements that are required in order

      * to perform Tarjan computation of strongly connected components.

      */

     public static abstract class TarjanNode<D> extends Node<D> implements Comparable<TarjanNode<D>> {

         int index = -1;

         int lowlink;

         boolean active;

         public TarjanNode(D data) {

             super(data);

         }

         public abstract Iterable<? extends TarjanNode<D>> getDependencies();

         public int compareTo(TarjanNode<D> o) {

             return (index < o.index) ? -1 : (index == o.index) ? 0 : 1;

         }

     }

     /**

      * Tarjan's algorithm to determine strongly connected components of a

      * directed graph in linear time. Works on TarjanNode.

      */

     public static <D, N extends TarjanNode<D>> List<? extends List<? extends N>> tarjan(Iterable<? extends N> nodes) {

         ListBuffer<List<N>> cycles = ListBuffer.lb();

         ListBuffer<N> stack = ListBuffer.lb();

         int index = 0;

         for (N node: nodes) {

             if (node.index == -1) {

                 index += tarjan(node, index, stack, cycles);

             }

         }

         return cycles.toList();

     }

     private static <D, N extends TarjanNode<D>> int tarjan(N v, int index, ListBuffer<N> stack, ListBuffer<List<N>> cycles) {

         v.index = index;

         v.lowlink = index;

         index++;

         stack.prepend(v);

         v.active = true;

         for (TarjanNode<D> nd: v.getDependencies()) {

             @SuppressWarnings("unchecked")

             N n = (N)nd;

             if (n.index == -1) {

                 tarjan(n, index, stack, cycles);

                 v.lowlink = Math.min(v.lowlink, n.lowlink);

             } else if (stack.contains(n)) {

                 v.lowlink = Math.min(v.lowlink, n.index);

             }

         }

         if (v.lowlink == v.index) {

             N n;

             ListBuffer<N> cycle = ListBuffer.lb();

             do {

                 n = stack.remove();

                 n.active = false;

                 cycle.add(n);

             } while (n != v);

             cycles.add(cycle.toList());

         }

         return index;

     }

     /**

      * Debugging: dot representation of a set of connected nodes. The resulting

      * dot representation will use {@code Node.toString} to display node labels

      * and {@code Node.printDependency} to display edge labels. The resulting

      * representation is also customizable with a graph name and a header.

      */

     public static <D> String toDot(Iterable<? extends TarjanNode<D>> nodes, String name, String header) {

         StringBuilder buf = new StringBuilder();

         buf.append(String.format("digraph %s {\n", name));

         buf.append(String.format("label = \"%s\";\n", header));

         //dump nodes

         for (TarjanNode<D> n : nodes) {

             buf.append(String.format("%s [label = \"%s\"];\n", n.hashCode(), n.toString()));

         }

         //dump arcs

         for (TarjanNode<D> from : nodes) {

             for (TarjanNode<D> to : from.getDependencies()) {

                 buf.append(String.format("%s -> %s [label = \" %s \"];\n",

                         from.hashCode(), to.hashCode(), from.printDependency(to)));

             }

         }

         buf.append("}\n");

         return buf.toString();

     }

 }