Comparable vs Comparator in Java

1. Comparable:

   • The Comparable interface is part of the Java language itself, and it is found in the java.lang package.

   • When a class implements the Comparable interface, it means that instances of that class can be compared to each other for the purpose of natural ordering.

   • The Comparable interface has one method, compareTo, which takes another object of the same class as an argument and returns an integer value. This method should be implemented to specify the natural ordering of objects.

   • The natural ordering is the default ordering for objects of the class when sorting without explicitly specifying a Comparator.

Example:

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

        // Constructors, getters, setters...

        @Override
        public int compareTo(Person otherPerson) {
            // Implement comparison logic based on age
            return Integer.compare(this.age, otherPerson.age);
        }
    }

1. Comparator:

   • The Comparator interface is a more flexible way to define custom sorting orders for objects. It can be used to sort objects of classes that you cannot modify (e.g., classes from external libraries) or to define multiple sorting orders for a class.

   • To use a Comparator, you create a separate class or lambda expression that implements the Comparator interface and provides the sorting logic.

   • The Comparator interface has one method, compare, which takes two objects of the class being sorted and returns an integer value to indicate their relative order.

Example:

    // Define a Comparator for sorting Person objects by name
    public class PersonNameComparator implements Comparator<Person> {
        @Override
        public int compare(Person person1, Person person2) {
            return person1.getName().compareTo(person2.getName());
        }
    }

    // Sorting using the PersonNameComparator
    List<Person> people = new ArrayList<>();
    // Add people to the list
    Collections.sort(people, new PersonNameComparator());

In summary, Comparable is used for defining the natural ordering of objects within a class, while Comparator is used to define custom sorting orders for objects, either by implementing a separate comparator class or using lambda expressions. The choice between Comparable and Comparator depends on whether you have control over the class being sorted and whether you need to define multiple sorting orders.