@Override
  public int compare(final Double d1, final Double d2) {
    if (d1 == null ^ d2 == null) {
      return d1 == null ? -1 : 1; // either of one is null.
    } else if (d1 == null) return 0; // both are null
    return d1.compareTo(d2); // natural ordering.
  }
a concrete column interpreter implementation. The cell value is a Double value and its promoted
data type is also a Double value. For computing aggregation function, this class is used to find
the datatype of the cell value. Client is supposed to instantiate it and passed along as a
parameter. See TestDoubleColumnInterpreter methods for its sample usage. Its methods handle null
arguments gracefully.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/coprocessor/DoubleColumnInterpreter.java