Why do we use BitSet class ?

[Vikas Khengare]

Hi Friends........
 
    I am very New to Lucene World !!! As this world is interesting to me
So I want to go in deep level of it to realize the beauty of it.
So can you help me to realize that beauty ?
 
    I have question 
 
1] Why do use BitSet Class ?
2] Is it required in Filtering / Sorting of results or to Index ?
3] What do you means by Inverted Index ?
4] Can we give limit to no. of hits returned by Searcher.
 
Thanks.
 
Best Regards
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