How do we handle duplicates with separate chaining?

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How do we handle duplicates with separate
chaining?
How do we handle deletions?
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7. What is the advantage of a hash table?
O(1) complexity to search for or insert an item
(i.e. constant time regardless of the number of
items).
8. Disadvantage?
Must know size of array needed in advance (in
Java arrays can not be resized - another bigger
array would be needed). This problem is reduced
when separate chaining is used.
Also, there is no way to access items in order.