How to Sort TreeSet Elements using Comparable Interface in Java?
Last Updated :
01 Oct, 2021
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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 program to demonstrate how to Sort TreeSet using
// Comparable interface in ascending order
import java.util.*;
// 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 TreeSet in
// ascending order
public int compareTo(Student stu)
{
return this.marks.compareTo(stu.marks);
}
}
class GFG {
public static void main(String[] args)
{
// New TreeSet
TreeSet<Student> set = new TreeSet<>();
// 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));
// 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:
// Java program demonstrate how to Sort TreeSet using
// Comparable interface in descending order
import java.util.*;
// 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 TreeSet in
// descending order
public int compareTo(Student stu)
{
return stu.marks.compareTo(this.marks);
}
}
class GFG {
public static void main(String[] args)
{
// New TreeSet
TreeSet<Student> set = new TreeSet<>();
// 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));
// 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]
