Returns a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive. (If fromKey and toKey are equal, the returned map is empty.) 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 IllegalArgumentException on an attempt to insert a key outside its range.

Parameters:

fromKey		low endpoint (inclusive) of the keys in the returned map
toKey		high endpoint (exclusive) of the keys in the returned map

Returns:  a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive

Exceptions:

ClassCastException		if fromKey and toKey cannot be compared to one another using this map's comparator (or, if the map has no comparator, using natural ordering). Implementations may, but are not required to, throw this exception if fromKey or toKey cannot be compared to keys currently in the map.
NullPointerException		if fromKey or toKey is null and this map does not permit null keys
IllegalArgumentException		if fromKey is greater than toKey; or if this map itself has a restricted range, and fromKey or toKey lies outside the bounds of the range