@Override
    public String toString() {
        return "PlacementSpec" +
            "(startPartition=" + startPartition +
            ", numPartitions=" + numPartitions +
            ", numReplicas=" + numReplicas +
            ")";
    }
Specifies a replica placement that we want to make.
metadata/src/main/java/org/apache/kafka/metadata/placement/PlacementSpec.java