IComparer Interface (System.Collections)

IComparer Interface

Assembly: System.dll

public interface IComparer

Description

Provides a generalized comparison contract that defines a single method for comparing two objects. This interface is used to create custom comparers for sorting or maintaining the order of collections.

Members

Methods

int Compare(object x, object y)

Parameters

x The first object to compare.
y The second object to compare.

Returns

int
A signed integer that indicates the relative order of the objects being compared.
- Less than zero: x is less than y.
- Zero: x is equal to y.
- Greater than zero: x is greater than y.

Remarks

The Compare method is used by sorting algorithms and data structures that require ordering. For example, the Array.Sort(Array, IComparer) method uses this interface to sort an array of objects. When implementing IComparer, you should ensure that the comparison is transitive (if a is less than b, and b is less than c, then a must be less than c), symmetric (if a is equal to b, then b is equal to a), and reflexive (a is equal to a).

Example

The following example demonstrates how to implement the IComparer interface to sort a collection of strings by their length.

using System;
using System.Collections;
using System.Collections.Generic;

public class StringLengthComparer : IComparer
{
    public int Compare(object x, object y)
    {
        string s1 = x as string;
        string s2 = y as string;

        if (s1 == null || s2 == null)
        {
            throw new ArgumentException("Input must be strings.");
        }

        if (s1.Length < s2.Length)
        {
            return -1;
        }
        else if (s1.Length > s2.Length)
        {
            return 1;
        }
        else
        {
            return 0;
        }
    }
}

public class Example
{
    public static void Main(string[] args)
    {
        string[] words = { "apple", "banana", "kiwi", "orange", "grape" };
        Array.Sort(words, new StringLengthComparer());

        Console.WriteLine("Sorted by length:");
        foreach (string word in words)
        {
            Console.WriteLine(word);
        }
    }
}

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