Sorting Objects: Comparable<T> and Comparator<T>

Intermediate14 min read•Updated: 2026-10-22

🔀 Sorting Objects: Comparable vs Comparator

Introduction

Sorting primitives is straightforward, but sorting domain objects (like Student by GPA, roll number, or name) requires defining comparison logic through Comparable (natural order) or Comparator (custom multiple sort strategies).

🆚 Comparable vs Comparator

Comparable<T>: Implemented inside the domain class itself via compareTo(T other).
Comparator<T>: Separate standalone comparison logic (often written as modern lambda expressions: Comparator.comparing(Student::getGpa)).

1import java.util.ArrayList;
2import java.util.Collections;
3import java.util.Comparator;
4import java.util.List;
5 
6class Student implements Comparable<Student> {
7    int roll;
8    String name;
9    double gpa;
10 
11    public Student(int r, String n, double g) {
12        this.roll = r; this.name = n; this.gpa = g;
13    }
14 
15    // Natural ordering: by Roll Number ascending
16    @Override
17    public int compareTo(Student other) {
18        return Integer.compare(this.roll, other.roll);
19    }
20 
21    public double getGpa() { return gpa; }
22    public String getName() { return name; }
23    @Override public String toString() { return name + " (" + gpa + ")"; }
24}
25 
26public class SortingDemo {
27    public static void main(String[] args) {
28        List<Student> students = new ArrayList<>();
29        students.add(new Student(105, "Deepak", 7.8));
30        students.add(new Student(101, "Ananya", 9.6));
31        students.add(new Student(103, "Vikram", 8.4));
32 
33        // 1. Natural Sort (Roll Number via Comparable):
34        Collections.sort(students);
35 
36        // 2. Custom Sort: Highest GPA first using Modern Comparator lambda:
37        students.sort(Comparator.comparingDouble(Student::getGpa).reversed());
38 
39        System.out.println("Sorted by Highest GPA: " + students);
40    }
41}

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Map Interface: HashMap Internal Working (Buckets, Hash Codes, Collisions)

Sorting Objects: Comparable<T> and Comparator<T>

Intermediate14 min read•Updated: 2026-10-22

Study Materials

🔀 Sorting Objects: Comparable vs Comparator

Introduction

🆚 Comparable vs Comparator

Comparable<T>: Implemented inside the domain class itself via compareTo(T other).
Comparator<T>: Separate standalone comparison logic (often written as modern lambda expressions: Comparator.comparing(Student::getGpa)).

1import java.util.ArrayList;
2import java.util.Collections;
3import java.util.Comparator;
4import java.util.List;
5 
6class Student implements Comparable<Student> {
7    int roll;
8    String name;
9    double gpa;
10 
11    public Student(int r, String n, double g) {
12        this.roll = r; this.name = n; this.gpa = g;
13    }
14 
15    // Natural ordering: by Roll Number ascending
16    @Override
17    public int compareTo(Student other) {
18        return Integer.compare(this.roll, other.roll);
19    }
20 
21    public double getGpa() { return gpa; }
22    public String getName() { return name; }
23    @Override public String toString() { return name + " (" + gpa + ")"; }
24}
25 
26public class SortingDemo {
27    public static void main(String[] args) {
28        List<Student> students = new ArrayList<>();
29        students.add(new Student(105, "Deepak", 7.8));
30        students.add(new Student(101, "Ananya", 9.6));
31        students.add(new Student(103, "Vikram", 8.4));
32 
33        // 1. Natural Sort (Roll Number via Comparable):
34        Collections.sort(students);
35 
36        // 2. Custom Sort: Highest GPA first using Modern Comparator lambda:
37        students.sort(Comparator.comparingDouble(Student::getGpa).reversed());
38 
39        System.out.println("Sorted by Highest GPA: " + students);
40    }
41}

Next Lesson

Map Interface: HashMap Internal Working (Buckets, Hash Codes, Collisions)

Continue learning with hands-on practice, examples, and exercises in the upcoming topic.

Related Lessons

Previous Lesson	Next Lesson
Iterators, ListIterators, and ConcurrentModificationException	Map Interface: HashMap Internal Working (Buckets, Hash Codes, Collisions)

Practice Quiz

Test your understanding of this lesson with 1 questions. Each question has one correct answer.

Previous Next