Java TreeSet
Java TreeSet
A TreeSet is a collection that stores unique elements in sorted order.
It is part of the java.util package and implements the Set interface.
Tip: Unlike HashSet, which has no order, TreeSet keeps its elements sorted automatically.
Create a TreeSet
Example
Create a TreeSet object called cars that will store strings:
import java.util.TreeSet; // Import the TreeSet class
TreeSet<String> cars = new TreeSet<>();Now you can use methods like add(), contains(), and remove() to manage your sorted set of elements.
Add Elements
To add elements to a TreeSet, use the add() method:
Example
import java.util.TreeSet;
public class Main {
public static void main(String[] args) {
TreeSet<String> cars = new TreeSet<>();
cars.add("Volvo");
cars.add("BMW");
cars.add("Ford");
cars.add("BMW"); // Duplicate
cars.add("Mazda");
System.out.println(cars);
}
}Output: The elements will be sorted automatically (e.g., [BMW, Ford, Mazda, Volvo]).
Note: Duplicates like "BMW" will only appear once.
Check if an Element Exists
Use contains() to check if an element exists:
Remove an Element
Use remove() to remove an element:
Remove All Elements
Use clear() to remove all elements:
TreeSet Size
Use size() to count how many unique elements are in the set:
Note: Duplicate values are not counted - only unique elements are included in the size.
Loop Through a TreeSet
Loop through the elements of a TreeSet with a for-each loop:
Example
TreeSet<String> cars = new TreeSet<>();
// add elements...
for (String i : cars) {
System.out.println(i);
}Using TreeSet with Numbers
TreeSet also works with numbers and sorts them from smallest to largest:
Example
import java.util.TreeSet;
public class Main {
public static void main(String[] args) {
TreeSet<Integer> numbers = new TreeSet<>();
numbers.add(40);
numbers.add(10);
numbers.add(30);
numbers.add(20);
for (int n : numbers) {
System.out.println(n);
}
}
}Output: The numbers will be printed in sorted order (10, 20, 30, 40).
HashSet vs TreeSet
| Feature | HashSet |
TreeSet |
|---|---|---|
| Order | No guaranteed order | Sorted (natural order) |
| Duplicates | Not allowed | Not allowed |
| Performance | Faster (no sorting) | Slower (due to sorting) |
Tip: Use HashSet when you care about speed, and TreeSet when you need sorted elements.
