Difference between Comparable and Comparator

Comparable and Comparator are two Java interfaces that allow objects to be compared and sorted.

Comparable

• Comparable is a functional interface that is implemented by a class to define its natural ordering.
• The compareTo method of the Comparable interface compares an object with another object and returns an integer indicating their relative order.

class Person implements Comparable<Person> {
  private String name;
  private int age;

  public Person(String name, int age) {
    this.name = name;
    this.age = age;
  }

  public int compareTo(Person other) {
    if (this.age != other.age) {
      return Integer.compare(this.age, other.age);
    } else {
      return this.name.compareTo(other.name);
    }
  }
}

Comparator

Comparator, on the other hand, is a functional interface that is used to provide custom comparison logic, separate from the class’s natural ordering. The compare method of the Comparator interface takes two objects and returns an integer indicating their relative order.

class Person {
  private String name;
  private int age;

  public Person(String name, int age) {
    this.name = name;
    this.age = age;
  }
}

class PersonAgeComparator implements Comparator<Person> {
  public int compare(Person p1, Person p2) {
    return Integer.compare(p1.age, p2.age);
  }
}

class PersonNameComparator implements Comparator<Person> {
  public int compare(Person p1, Person p2) {
    return p1.name.compareTo(p2.name);
  }
}

In summary, Comparable is used for objects to define their natural ordering, while Comparator is used for custom comparison logic, separate from the object’s natural ordering.