IComparable & IComparer Interfaces

IComparable & IComparer Interfaces are used to provide comparison mechanism to collection of objects that comparison scheme is used by the collection for sorting functions.

IComparable: It defines a way of comparison for two similar class objects. A collection of objects internally uses this defined way to sort objects.
Using IComparable we can define only one way of comparison for a collection of objects.
This is internal comparer
We defines CompareTo method of IComparable  that returns int

            public int CompareTo(object obj)

            {

                return this.Age.CompareTo(((Person)obj).Age);

            }

IComparer: It defines multiple ways of comparison for two similar class objects.
Using IComparer we can define multiple ways of comparison for a collection of objects.
This comparison take place externally
We defines Compare method of IComparer that returns int

            public int Compare(Student x, Student y)

            {

                return string.Compare(x.Name, y.Name);

            }

Source Code:

        #region IComparable

        public class Person : IComparable

        {

            public string Name { get; set; }

            public int Age { get; set; }

            public int CompareTo(object obj)

            {

                return this.Age.CompareTo(((Person)obj).Age);

            }

        }

        //Generic Icomparable example

        public class Employee : IComparable<Employee>

        {

            public string Name { get; set; }

            public int Salary { get; set; }

           

            public int CompareTo(Employee other)

            {

                return this.Salary.CompareTo(other.Salary);

            }

        }

        #endregion

        #region IComparer

        public class Student

        {

            public string Name { get; set; }

            public double Percentile { get; set; }

        }

        public class SortByName : IComparer<Student>

        {

            public int Compare(Student x, Student y)

            {

                return string.Compare(x.Name, y.Name);

            }

        }

        public class SortByPercentile : IComparer<Student>

        {

            public int Compare(Student x, Student y)

            {

                if (x.Percentile == y.Percentile)

                    return 0;

                else if (x.Percentile > y.Percentile)

                    return 1;

                else

                    return -1;

            }

        }

        #endregion

Client Code:

        static void Main(string[] args)

        {

            #region IComparable

            Person me = new Person { Name = "Anand", Age = 32 };

            Person MyFather = new Person { Name = "PSTomar", Age = 65 };

            Person MyGrandFather = new Person { Name = "DSTomar", Age = 85 };

            List<Person> lstPerson = new List<Person>();

            lstPerson.Add(MyFather);

            lstPerson.Add(me);

            lstPerson.Add(MyGrandFather);

            lstPerson.Sort();

            Console.WriteLine("Result of IComparable example :");

            foreach (Person p in lstPerson)

                Console.WriteLine("Name : {0}, Age : {1} ", p.Name, p.Age);

            Console.ReadLine();

            #endregion

            #region IComparer

            Student Megha = new Student { Name = "Megha", Percentile = 32.55 };

            Student Renuka = new Student { Name = "Renuka", Percentile = 65.12 };

            Student Ghanshyam = new Student { Name = "Ghanshyam", Percentile = 80.11 };

            List<Student> lstStudent = new List<Student>();

            lstStudent.Add(Megha);

            lstStudent.Add(Renuka);

            lstStudent.Add(Ghanshyam);

            lstStudent.Sort(new SortByName());

            Console.WriteLine("Result of IComparer example :");

            foreach (Student p in lstStudent)

                Console.WriteLine("Name : {0}, Percentile : {1} ", p.Name, p.Percentile);

            Console.ReadLine();

           

            lstStudent.Sort(new SortByPercentile());

            foreach (Student p in lstStudent)

                Console.WriteLine("Name : {0}, Percentile : {1} ", p.Name, p.Percentile);

            Console.ReadLine();

            #endregion

        }