/**
* Adds an outgoing arc to the specified vertex. Also calls {@link #addIncomingArcTo} for
* <tt>headVertex</tt> with <tt>this</tt> as the argument. Does nothing if <tt>headVertex</tt> is
* the head vertex of an already existing outgoing arc.
*
* @param headVertex Head vertex to be added to establish a new outgoing arc. <tt>Null</tt> is not
* allowed.
*/
public void addOutgoingArcTo(Vertex headVertex) {
if (!_heads.contains(headVertex)) {
_heads.add(headVertex);
headVertex.addIncomingArcTo(this);
}
}
