What is the Comparable interface and how is it used?

The Comparable interface in Java is used to define the natural ordering of objects of a class. It contains the method compareTo(T o), which compares the current object with the object o and returns:

• a negative number if the current object is less than o
• zero if the objects are equal
• a positive number if the current object is greater than o

This allows sorting collections of objects, for example, using Collections.sort().

Example of usage:

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

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

    @Override
    public int compareTo(Person other) {
        return Integer.compare(this.age, other.age); // sorting by age
    }
}

// Usage:
List<Person> people = new ArrayList<>();
people.add(new Person("Alice", 30));
people.add(new Person("Bob", 25));
Collections.sort(people); // will sort by age