@Override
    public void setTraversal(final Traversal.Admin<?, ?> parentTraversal) {
        super.setTraversal(parentTraversal);
        this.integrateChild(this.targetVertexFilter.get());
        this.integrateChild(this.edgeTraversal.get());
        this.integrateChild(this.distanceTraversal.get());
    }
@author Daniel Kuppitz (http://gremlin.guru)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/traversal/step/map/ShortestPathVertexProgramStep.java