HashSet, TreeSet

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HashSet, TreeSet

In Java, both HashSet and TreeSet are part of the Java Collection Framework and implement the Set interface. A Set is a collection that does not allow duplicate elements.

🔹 HashSet:

HashSet is backed by a hash table (actually a HashMap).

It does not maintain any order of elements.

It allows null elements (only one).

Operations like add, remove, contains are performed in constant time O(1).

Suitable when you want fast access and do not care about order.

Example:

java

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HashSet<String> set = new HashSet<>();

set.add("Apple");

set.add("Banana");

set.add("Apple"); // Duplicate, will be ignored

🔹 TreeSet:

TreeSet is implemented using a Red-Black Tree (a self-balancing binary search tree).

It maintains elements in ascending (natural) order.

Does not allow null elements (throws NullPointerException).

Operations take O(log n) time due to tree traversal.

Suitable when you need sorted data without duplicates.

Example:

java

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TreeSet<String> treeSet = new TreeSet<>();

treeSet.add("Orange");

treeSet.add("Apple");

treeSet.add("Banana"); // Automatically sorted

🔸 Key Differences:

Feature HashSet TreeSet

Order Unordered Sorted

Performance Faster (O(1)) Slower (O(log n))

Null allowed Yes No

In summary, use HashSet for speed and TreeSet for sorted elements.

In summary, use HashSet for speed and TreeSet for sorted elements.

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Final Keyword

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