Try It Yourself - SyntaxStudy Editor

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import java.util.*;

class Student implements Comparable<Student> {
    String name;
    double gpa;

Student(String name, double gpa) {
        this.name = name;
        this.gpa  = gpa;
    }

@Override
    public int compareTo(Student other) {
        // Natural order: ascending by name
        return this.name.compareTo(other.name);
    }

@Override
    public String toString() {
        return name + "(" + gpa + ")";
    }
}

public class ComparableDemo {
    public static void main(String[] args) {
        List<Student> students = new ArrayList<>(List.of(
            new Student("Zoe",   3.8),
            new Student("Alice", 3.5),
            new Student("Bob",   3.9),
            new Student("Carol", 3.5)
        ));

// Natural ordering (Comparable)
        Collections.sort(students);
        System.out.println("By name: " + students);

// Comparator: descending GPA, then name
        Comparator<Student> byGpaDesc = Comparator
            .comparingDouble(Student::gpa)
            .reversed()
            .thenComparing(s -> s.name);

students.sort(byGpaDesc);
        System.out.println("By GPA desc: " + students);

// TreeSet uses natural order
        TreeSet<Student> tree = new TreeSet<>(students);
        System.out.println("TreeSet first: " + tree.first());
    }
}