Java TreeSet
Sorted collection that maintains unique elements automatically
🌳 What is TreeSet?
TreeSet is a sorted collection in Java that automatically arranges elements in ascending order and prevents duplicates. It's perfect when you need unique, sorted data storage.
// Simple TreeSet example
TreeSet<Integer> numbers = new TreeSet<>();
numbers.add(5);
numbers.add(2);
numbers.add(8);
System.out.println(numbers); // [2, 5, 8]
TreeSet Key Features
Auto-Sorting
Elements are automatically sorted
TreeSet<String> names = new TreeSet<>();
names.add("Charlie");
names.add("Alice");
names.add("Bob");
// Output: [Alice, Bob, Charlie]No Duplicates
Automatically removes duplicate values
TreeSet<Integer> set = new TreeSet<>();
set.add(1);
set.add(1); // Duplicate ignored
set.add(2);
// Output: [1, 2]Fast Operations
Efficient search, insert, and delete
TreeSet<Integer> set = new TreeSet<>();
set.add(10);
boolean exists = set.contains(10); // true
set.remove(10);
// All operations are O(log n)Range Operations
Get subsets within ranges
TreeSet<Integer> set = new TreeSet<>();
set.addAll(Arrays.asList(1,3,5,7,9));
SortedSet<Integer> subset = set.subSet(3, 8);
// Output: [3, 5, 7]🔹 Creating and Using TreeSet
Here's how to create and work with TreeSet:
import java.util.*;
public class TreeSetExample {
public static void main(String[] args) {
// Create a TreeSet
TreeSet<String> fruits = new TreeSet<>();
// Add elements
fruits.add("Apple");
fruits.add("Banana");
fruits.add("Cherry");
fruits.add("Apple"); // Duplicate - will be ignored
// Display sorted elements
System.out.println("Fruits: " + fruits);
// Output: [Apple, Banana, Cherry]
// Check if element exists
if (fruits.contains("Banana")) {
System.out.println("Banana is in the set");
}
// Remove element
fruits.remove("Banana");
System.out.println("After removal: " + fruits);
}
}Output:
Fruits: [Apple, Banana, Cherry]
Banana is in the set
After removal: [Apple, Cherry]
🔹 TreeSet with Custom Objects
Use TreeSet with custom objects by implementing Comparable:
class Student implements Comparable<Student> {
String name;
int age;
Student(String name, int age) {
this.name = name;
this.age = age;
}
@Override
public int compareTo(Student other) {
return this.age - other.age; // Sort by age
}
@Override
public String toString() {
return name + "(" + age + ")";
}
}
// Usage
TreeSet<Student> students = new TreeSet<>();
students.add(new Student("Alice", 20));
students.add(new Student("Bob", 18));
students.add(new Student("Charlie", 22));
System.out.println(students);
// Output: [Bob(18), Alice(20), Charlie(22)]Output:
[Bob(18), Alice(20), Charlie(22)]
🔹 Common TreeSet Methods
Essential methods for working with TreeSet:
TreeSet<Integer> numbers = new TreeSet<>();
numbers.addAll(Arrays.asList(5, 2, 8, 1, 9, 3));
// Basic operations
System.out.println("Size: " + numbers.size()); // 6
System.out.println("First: " + numbers.first()); // 1
System.out.println("Last: " + numbers.last()); // 9
// Range operations
System.out.println("Lower than 5: " + numbers.headSet(5)); // [1, 2, 3]
System.out.println("5 and higher: " + numbers.tailSet(5)); // [5, 8, 9]
System.out.println("Between 2 and 8: " + numbers.subSet(2, 8)); // [2, 3, 5]
// Navigation
System.out.println("Higher than 5: " + numbers.higher(5)); // 8
System.out.println("Lower than 5: " + numbers.lower(5)); // 3Output:
Size: 6
First: 1
Last: 9
Lower than 5: [1, 2, 3]
5 and higher: [5, 8, 9]
Between 2 and 8: [2, 3, 5]
Higher than 5: 8
Lower than 5: 3