Lesson 38: Working with the Set Interface

The Set interface models the mathematical concept of a set: an unordered collection that contains only unique elements.

1. HashSet

• Implementation: Uses a hash table for storage (relies on object hashing).
• Performance: Provides constant time (O(1)) performance for basic operations like add(), remove(), and contains(), assuming a good hash function.
• Order: Does not guarantee insertion order.

java import java.util.HashSet; import java.util.Set;

Set uniqueColors = new HashSet<>(); uniqueColors.add("Red"); uniqueColors.add("Blue"); boolean added = uniqueColors.add("Red"); // Returns false, Red already exists

System.out.println(uniqueColors.size()); // Output: 2

// Iterating a Set (order is not guaranteed) for (String color : uniqueColors) { System.out.println(color); }

2. LinkedHashSet

• Maintains insertion order (iterates in the order elements were added).
• Slightly slower than HashSet due to the overhead of maintaining the linked list structure.

3. TreeSet

• Implementation: Uses a tree structure (Red-Black Tree).
• Order: Stores elements in their natural sorted order (or by a custom Comparator).
• Performance: Operations are generally O(log N) (logarithmic time), making it slower than HashSet but necessary if sorted output is required.

java import java.util.TreeSet;

TreeSet sortedNumbers = new TreeSet<>(); sortedNumbers.add(50); sortedNumbers.add(10); sortedNumbers.add(30);

// Output: [10, 30, 50] (Always sorted) System.out.println(sortedNumbers);