TreeSet is an implementation of the SortedSet interface in Java that uses a Tree for storage. The ordering of the elements is maintained by a Set using their natural ordering whether an explicit comparator is provided.
To sort TreeSet elements using Comparable interface in java first, we create a class Student that implements the Comparable interface. In this class we override the compareTo() method.
Pseudo Code:
// Student class implements comparable interface
class Student implements Comparable<Student> {
Integer marks;
Student(Integer marks) {
this.marks = marks;
}
// override toString method
public String toString() {
return (" " + this.marks);
}
// Override compareTo method to sort LinkedHashSet in ascending order
public int compareTo(Student stu) {
return this.marks.compareTo(stu.marks);
}
}
Below is the implementation of the above approach:
Example 1:
Java
// Java program to demonstrate how to Sort TreeSet using// Comparable interface in ascending orderÂ
import java.util.*;Â
// Student class implements comparable interfaceclass Student implements Comparable<Student> {Â Â Â Â Â Â Â Integer marks;Â
    Student(Integer marks) { this.marks = marks; }Â
    // override toString method    public String toString() { return (" " + this.marks); }Â
    // Override compareTo method to sort TreeSet in    // ascending order    public int compareTo(Student stu)    {        return this.marks.compareTo(stu.marks);    }}Â
class GFG {Â Â Â Â public static void main(String[] args)Â Â Â Â {Â
        // New TreeSet        TreeSet<Student> set = new TreeSet<>();Â
        // Adding elements to the set        set.add(new Student(500));        set.add(new Student(300));        set.add(new Student(400));        set.add(new Student(100));        set.add(new Student(200));Â
        // Print TreeSet sorted in ascending order        System.out.println("Sort elements in ascending order : " + set);           }} |
Output
Sort elements in ascending order : [ 100, 200, 300, 400, 500]
Example 2:Â
Java
// Java program demonstrate how to Sort TreeSet using// Comparable interface in descending orderÂ
import java.util.*;Â
// Student class implements comparable interfaceclass Student implements Comparable<Student> {Â Â Â Â Â Â Â Integer marks;Â
    Student(Integer marks) { this.marks = marks; }Â
    // override toString method    public String toString() { return (" " + this.marks); }Â
    // Override compareTo method to sort TreeSet in    // descending order    public int compareTo(Student stu)    {        return stu.marks.compareTo(this.marks);    }}Â
class GFG {Â Â Â Â public static void main(String[] args)Â Â Â Â {Â
        // New TreeSet        TreeSet<Student> set = new TreeSet<>();Â
        // Adding elements to the set        set.add(new Student(500));        set.add(new Student(300));        set.add(new Student(400));        set.add(new Student(100));        set.add(new Student(200));Â
        // Print TreeSet sorted in descending order        System.out.println("Sort elements in descending order : " + set);           }} |
Output
Sort elements in descending order : [ 500, 400, 300, 200, 100]
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