Question

1.When using Java’s HashSet, how can one influence the data structure’s performance and space use?

2. How are the TreeMap and TreeSet classes in Java related?

Answer 1

`Hey,

Note: Brother in case of any queries, just comment in box I would be very happy to assist all your queries

The HashSet class implements the Set interface, backed by a hash table which is actually a HashMap instance. The maintenance of constant time performance, iterating over HashSet requires time proportional to the sum of the HashSet instance’s size (the number of elements) plus the “capacity” of the backing HashMap instance (the number of buckets). Thus, it’s very important not to set the initial capacity too high (or the load factor too low) if iteration performance is important.

Load factor and initial capacity are two main factors that affect the performance of HashSet operations. Load factor of 0.75 provides very effective performance as respect to time and space complexity. If we increase the load factor value more than that then memory overhead will be reduced (because it will decrease internal rebuilding operation) but, it will affect the add and search operation in hashtable. To reduce the rehashing operation we should choose initial capacity wisely. If initial capacity is greater than the maximum number of entries divided by the load factor, no rehash operation will ever occur.

2)

1) Both TreeMap and TreeSet are sorted data structure, which means they keep there element in predefined Sorted order. Sorting order can be natural sorting order defined by Comparable interface or custom sorting Order defined by Comparator interface. Both TreeMap and TreeSet has overloaded constructor which accept a Comparator, if provided all elements inside TreeSet or TreeMap will be compared and Sorted using this Comparator.

2) Both TreeSet and TreeMap implements base interfaces e.g. TreeSet implements Collection and Set interface so that they can be passed to method where a Collection is expected and TreeMap implements java.util.Map interface, which means you can pass it when a Map is expected.

3) TreeSet is practically implemented using TreeMap instance, similar to HashSet which is internally backed by HashMap instance. See my post Internal Implementation of HashSet to learn more.

4) Both TreeMap and TreeSet are non synchronized Collection, hence can not be shared between multiple threads. You can make both TreeSet and TreeMap synchronized by wrapping them into Synchronized collection by calling Collections.synchroinzedMap() method.

Kindly revert for any queries

Thanks.