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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.
/*
========================================================================
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.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Objects;
import java.util.Stack;
/**
* Implementation of
* Tarjan's algorithm
*
* @author Sualeh Fatehi
* @param
* Any comparable class
*/
public class TarjanStronglyConnectedComponentFinder>
{
private final DirectedGraph graph;
private final Collection> stronglyConnectedComponents;
private final Stack> stack;
public TarjanStronglyConnectedComponentFinder(final DirectedGraph graph)
{
this.graph = Objects.requireNonNull(graph);
stronglyConnectedComponents = new HashSet<>();
stack = new Stack>();
}
/**
* Calculates the sets of strongly connected vertices.
*
* @param graph
* Graph to detect cycles within.
* @return Set of strongly connected components (sets of vertices)
*/
public Collection> detectCycles()
{
for (final Vertex vertex: graph.vertexSet())
{
if (!vertex.hasAttribute("index"))
{
strongConnect(vertex, 0);
}
}
return stronglyConnectedComponents;
}
private void strongConnect(final Vertex vertexFrom, final int index)
{
vertexFrom.putAttribute("index", index);
vertexFrom.putAttribute("lowlink", index);
stack.push(vertexFrom);
for (final DirectedEdge edge: graph.getOutgoingEdges(vertexFrom))
{
final Vertex vertexTo = edge.getTo();
if (!vertexTo.hasAttribute("index"))
{
// Successor vertex has not yet been visited; recurse on it
strongConnect(vertexTo, index + 1);
vertexFrom.putAttribute("lowlink",
Math.min(vertexFrom.getAttribute("lowlink"),
vertexTo.getAttribute("lowlink")));
}
else if (stack.contains(vertexTo))
{
// Successor vertex is on stack, hence in the current SCC
vertexFrom.putAttribute("lowlink",
Math.min(vertexFrom.getAttribute("lowlink"),
vertexTo.getAttribute("index")));
}
}
if (vertexFrom.getAttribute("lowlink") == vertexFrom.getAttribute("index"))
{
final LinkedList scc = new LinkedList<>();
Vertex sccVertex;
do
{
sccVertex = stack.pop();
scc.addFirst(sccVertex.getValue());
} while (!vertexFrom.equals(sccVertex));
if (scc.size() > 1)
{
stronglyConnectedComponents.add(scc);
}
}
}
}