comparators in java

 

import java.util.*;

public class Comparators {

    public static void main(String[] args) {

        ArrayList<Person> list = new ArrayList<Person>();

        list.add(new Person("ashwith", 34));

        list.add(new Person("abhi", 20));

        list.add(new Person("bharath", 24));

        list.add(new Person("vinay", 31));

        Collections.sort(list);

        System.out.println(list);

    }

}

class Person implements Comparable<Person> {

    String name;

    int age;

    Person(String name, int age) {

        this.name = name;

        this.age = age;

    }

    public int compareTo(Person person) {

        if (this.age == person.age) {

            return 0;

        } else {

            return (this.age < person.age ? -1 : 1);

        }

    }

    public String toString() {

        return this.name + ":" + this.age;

    }

}

DRYRUN:

1. Initialization:

   • An ArrayList named list is created to store Person objects.
   • Four Person objects are added to the list with names and ages:
     • “ashwith” (age 34)
     • “abhi” (age 20)
     • “bharath” (age 24)
     • “vinay” (age 31)

2. Sorting:

   • The Collections.sort(list) method is called to sort the list of Person objects.
   • The sorting is based on the compareTo method defined in the Person class.

3. compareTo Method:

   • The compareTo method compares two Person objects based on their ages.
   • If the ages are equal, it returns 0.
   • Otherwise, it returns -1 if the current person’s age is less than the other person’s age, and 1 otherwise.

4. Sorting Result:

   • After sorting, the list will be in ascending order of ages.
   • The sorted list will be printed using System.out.println(list).

Let’s apply the sorting logic step by step:

• Initially, the list contains:

  • “ashwith” (34)
  • “abhi” (20)
  • “bharath” (24)
  • “vinay” (31)

• Comparing “ashwith” (34) with “abhi” (20):

  • Since 34 > 20, “abhi” comes before “ashwith”.

• Comparing “abhi” (20) with “bharath” (24):

  • Since 20 < 24, “abhi” remains before “bharath”.

• Comparing “bharath” (24) with “vinay” (31):

  • Since 24 < 31, “bharath” remains before “vinay”.

• The sorted list will be:

  • “abhi” (20)
  • “bharath” (24)
  • “vinay” (31)
  • “ashwith” (34)

The output will be:

[abhi:20, bharath:24, vinay:31, ashwith:34