Returns a lexicographic-order comparator with a function that extracts a double sort key.

Parameters:

keyExtractor

the function used to extract the double sort key

Returns:  a lexicographic-order comparator composed of this and then the double sort key

Exceptions:

NullPointerException

if the argument is null.

See also:
comparingDouble(ToDoubleFunction), thenComparing(Comparator)

Since:  1.8

@implSpec This default implementation behaves as if thenComparing(comparingDouble(keyExtractor)).