Returns a view of the portion of this map whose keys are less than (or equal to, if {@code inclusive} is true) {@code toKey}. The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa. The returned map supports all optional map operations that this map supports.
The returned map will throw an {@code IllegalArgumentException}on an attempt to insert a key outside its range.
@param toKey high endpoint of the keys in the returned map
@param inclusive {@code true} if the high endpointis to be included in the returned view
@return a view of the portion of this map whose keys are less than(or equal to, if {@code inclusive} is true) {@code toKey}
@throws ClassCastException if {@code toKey} is not compatiblewith this map's comparator (or, if the map has no comparator, if {@code toKey} does not implement {@link Comparable}). Implementations may, but are not required to, throw this exception if {@code toKey} cannot be compared to keyscurrently in the map.
@throws NullPointerException if {@code toKey} is nulland this map does not permit null keys
@throws IllegalArgumentException if this map itself has arestricted range, and {@code toKey} lies outside thebounds of the range