public String getKey() {
        return this.key;
    }
A {@code VertexComputeKey} specifies a property of a vertex that will be used to store {@link GraphComputer} data.
If the VertexComputeKey is specified as transient, it will be dropped from the vertex prior to returning the {@link ComputerResult} graph.

@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/VertexComputeKey.java