public String getNextOpId(OpCode opCode) {
    return getNextOpId(opCode, null);
  }
Gets the unique ID for the next operator in the graph. The ID is of the following format:
jobName-jobId-opCode-nextOpNum;

@param opCode the {@link OpCode} of the next operator
@return the unique ID for the next operator in the graph
samza-core/src/main/java/org/apache/samza/application/descriptors/StreamApplicationDescriptorImpl.java