--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/src/share/classes/com/sun/tools/javac/util/GraphUtils.java	Tue Feb 12 19:25:09 2013 +0000
@@ -0,0 +1,145 @@
+/*
+ * 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();
+    }
+}