* Increases the capacity of and internally reorganizes this
* hashtable, in order to accommodate and access its entries more
* efficiently. This method is called automatically when the
* number of keys in the hashtable exceeds this hashtable's capacity
* and load factor.
protected void rehash()
The JavaDoc says it all. Besides, you can only invoke this method if you extend from Hashtable, since it's protected.
Most likely, you'll never need to deal with it (or even know of its existence).