Skip to main content

Java Exception Handling MCQ Test

  Loading…

Sorting using `Comparable` and `Comparator`

Sorting using `Comparable` and `Comparator` in Java provides flexibility in sorting objects based on natural ordering (defined by the object itself) or custom ordering (defined externally). Let's explain and demonstrate both:

Sorting Using Comparable:

1. Explanation:

   - Objects implementing `Comparable` interface provide a natural ordering based on their intrinsic properties.

   - The `compareTo()` method is overridden to define how objects should be compared to each other.


2. Demonstration:

   - Let's consider a class `Employee` with properties `id` and `name`. We'll implement `Comparable` to sort employees based on their ids.


   public class Employee implements Comparable<Employee> {

       private int id;

       private String name;


       // Constructor, getters, setters


       @Override

       public int compareTo(Employee other) {

           return Integer.compare(this.id, other.id);

       }

   }



   - Now, we can use `Arrays.sort()` to sort an array of `Employee` objects based on their ids.



   Employee[] employees = {emp1, emp2, emp3};

   Arrays.sort(employees);



Sorting Using Comparator:


1. Explanation:

   - `Comparator` interface provides a way to define custom sorting logic externally, independent of the object being sorted.

   - Custom `Comparator` implementations can be provided for different sorting criteria.


2. Demonstration:

   - Let's continue with the `Employee` class. Now, we want to sort employees based on their names. We'll implement a custom `Comparator` for this.



   public class NameComparator implements Comparator<Employee> {

       @Override

       public int compare(Employee emp1, Employee emp2) {

           return emp1.getName().compareTo(emp2.getName());

       }

   }



   - We can then use this comparator with `Arrays.sort()` to sort employees by name.



   Employee[] employees = {emp1, emp2, emp3};

   Arrays.sort(employees, new NameComparator());



Comparison:


- Comparable:

  - Used when objects have a natural ordering.

  - Changes to the class itself.

  - One default ordering.


- Comparator:

  - Used for custom ordering or when objects don't implement `Comparable`.

  - No changes to the class being sorted.

  - Multiple custom orderings possible.


Complete Example:


import java.util.Arrays;

import java.util.Comparator;


class Employee implements Comparable<Employee> {

    private int id;

    private String name;


    public Employee(int id, String name) {

        this.id = id;

        this.name = name;

    }


    // Getters, setters, etc.


    @Override

    public int compareTo(Employee other) {

        return Integer.compare(this.id, other.id);

    }


    @Override

    public String toString() {

        return "Employee{" +

                "id=" + id +

                ", name='" + name + '\'' +

                '}';

    }

}


class NameComparator implements Comparator<Employee> {

    @Override

    public int compare(Employee emp1, Employee emp2) {

        return emp1.getName().compareTo(emp2.getName());

    }

}


public class SortingDemo {

    public static void main(String[] args) {

        Employee[] employees = {

                new Employee(3, "John"),

                new Employee(1, "Alice"),

                new Employee(2, "Bob")

        };


        // Sorting using Comparable (by id)

        Arrays.sort(employees);

        System.out.println("Sorted by id:");

        for (Employee emp : employees) {

            System.out.println(emp);

        }


        // Sorting using Comparator (by name)

        Arrays.sort(employees, new NameComparator());

        System.out.println("\nSorted by name:");

        for (Employee emp : employees) {

            System.out.println(emp);

        }

    }

}



This example demonstrates sorting `Employee` objects both by their ids (using `Comparable`) and by their names (using `Comparator`).

Comments

Popular posts from this blog

Iterators and Collections

In Java, iterators are objects that allow for sequential access to the elements of a collection. The Java Collections Framework provides the Iterator interface, which defines methods for iterating over collections such as lists, sets, and maps. Here's an explanation of iterators and their relationship with collections, along with examples: Iterator Interface: The Iterator interface provides methods to iterate over the elements of a collection sequentially: - boolean hasNext(): Returns true if there are more elements to iterate over. - E next(): Returns the next element in the iteration. - void remove():  Removes the last element returned by `next()` from the underlying collection (optional operation). Collections and Iterators: 1. Collection Interface:    - Collections represent groups of objects, such as lists, sets, and maps.    - They provide methods for adding, removing, and accessing elements. 2. Iterator Usage:    - Collections implement the Iter...

The Collection Interface.

  The Collection Interface.