In Java, Hashtable has buckets whose quantity is equal to its capacity. Now how does it determine that it has to store an object in a particular bucket? I know it uses hashcode of the object but hashcode is a weird long string, what does hashtable do to the hashcode to determine place of entry?
Implementation-dependent (as in, if you rely on it working this way, your code is broken; the things HashMap guarantees are spelled out in its javadoc, and none of what I'm about to type is in there):
hashes are just a number. Between about -2billion and +2billion. That 'long weird string' you see is just a more convenient way to show it to you.
First, the higher digits of that number are mixed into the lower digits (actually, the higher bits are XORed into the lower ones): 12340005 is turned into 12341239.
Then, that number is divided by how many buckets there currently are, but the result is tossed out, it's the remainder we are interested in. This remainder is necessarily 0 or higher, and never more than '# of buckets there are', so always points exactly at one of the buckets.
That's the bucket that the object goes into.
if buckets grow too large, a resizing is done.
For more, well, HashMap is open source, as is HashSet - just have a look.