code: private File writeDotSourceToFile(String str) throws java.io.IOException,
  			GraphVizException
  	{
  		File temp;
  		try
  		{
  			temp = File.createTempFile("graph_", ".dot.tmp");
  			FileWriter fout = new FileWriter(temp);
  			fout.write(str);
  			fout.close();
  		} catch (Exception e)
  		{
  			throw new GraphVizException("Error: I/O error while writing the dot source to temp file!");
  		}
  		return temp;
  	}
docs: Writes the source of the graph in a file, and returns the written file as a File object.
  
  @param str
  Source of the graph (in dot language).
  @return The file (as a File object) that contains the source of the graph.
  @throws GraphVizException