Returns the adjacent floating point number to start in the direction of the second argument. If the arguments are equal, the second is returned. If either arg is #NaN => #NaN If both arguments are signed zeros => direction If start is +-Double/MIN_VALUE and direction would cause a smaller magnitude => zero with sign matching start If start is ##Inf or ##-Inf and direction would cause a smaller magnitude => Double/MAX_VALUE with same sign as start If start is equal to +=Double/MAX_VALUE and direction would cause a larger magnitude => ##Inf or ##-Inf with sign matching start See: https://docs.oracle.com/javase/8/docs/api/java/lang/Math.html#nextAfter-double-double-