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SchemaCrawler is an open-source Java API that makes working with database metadata as easy as working with plain old Java objects. SchemaCrawler is also a database schema discovery and comprehension, and schema documentation tool. You can search for database schema objects using regular expressions, and output the schema and data in a readable text format. The output is designed to be diff-ed against other database schemas.

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/*
========================================================================
SchemaCrawler
http://www.schemacrawler.com
Copyright (c) 2000-2016, Sualeh Fatehi .
All rights reserved.
------------------------------------------------------------------------

SchemaCrawler 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.

SchemaCrawler and the accompanying materials are made available under
the terms of the Eclipse Public License v1.0, GNU General Public License
v3 or GNU Lesser General Public License v3.

You may elect to redistribute this code under any of these licenses.

The Eclipse Public License is available at:
http://www.eclipse.org/legal/epl-v10.html

The GNU General Public License v3 and the GNU Lesser General Public
License v3 are available at:
http://www.gnu.org/licenses/

========================================================================
*/
package sf.util.graph;


import java.util.Collection;
import java.util.Objects;

public class SimpleCycleDetector>
{

  enum TraversalState
  {

   notStarted("white"),
   inProgress("lightgray"),
   marked("red"),
   complete("gray");

    private final String color;

    private TraversalState(final String color)
    {
      this.color = color;
    }

    public String getColor()
    {
      return color;
    }

  }

  private final DirectedGraph graph;

  public SimpleCycleDetector(final DirectedGraph graph)
  {
    this.graph = Objects.requireNonNull(graph);
  }

  /**
   * Checks if the graph contains a cycle.
   *
   * @return true if the graph contains a cycle, false otherwise
   */
  public boolean containsCycle()
  {
    final Collection> vertices = clearTraversalStates();
    for (final Vertex vertex: vertices)
    {
      if (vertex.getAttribute("traversalstate") == TraversalState.notStarted)
      {
        if (visitForCyles(vertex))
        {
          return true;
        }
      }
    }

    return false;
  }

  private Collection> clearTraversalStates()
  {
    final Collection> vertices = graph.vertexSet();
    for (final Vertex vertex: vertices)
    {
      vertex.putAttribute("traversalstate", TraversalState.notStarted);
    }
    return vertices;
  }

  private boolean visitForCyles(final Vertex vertex)
  {
    vertex.putAttribute("traversalstate", TraversalState.inProgress);

    for (final DirectedEdge edge: graph.edgeSet())
    {
      if (edge.isFrom(vertex))
      {
        final Vertex to = edge.getTo();
        if (to.getAttribute("traversalstate") == TraversalState.inProgress)
        {
          to.putAttribute("traversalstate", TraversalState.marked);
          return true;
        }
        else if (to.getAttribute("traversalstate") == TraversalState.notStarted)
        {
          if (visitForCyles(to))
          {
            return true;
          }
        }
      }
    }

    vertex.putAttribute("traversalstate", TraversalState.complete);

    return false;
  }

}