C# Equals Method: Check Whether Two Objects Are Equal

In C#, the Equals() method is used to determine whether two objects are equal based on their values. It is a member of the System.Object class, which means that all types in C# have an implementation of the Equals() method. In this tutorial, we'll cover how to use and override the Equals() method in custom classes to compare object equality.

Default behavior of the Equals() method:

By default, the Equals() method checks for reference equality, meaning it returns true if both objects being compared have the same memory address, and false otherwise. For value types, the default implementation checks for value equality. However, for custom reference types (classes), the default behavior may not be sufficient, and you might need to override the Equals() method to compare object values.

Overriding the Equals() method:

Consider a Person class with two properties, FirstName and LastName. We want to determine if two Person objects are equal based on their properties, not their references:

public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

To do this, we need to override the Equals() method in the Person class:

public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public override bool Equals(object obj)
    {
        // Check for null and type compatibility
        if (obj == null || GetType() != obj.GetType())
        {
            return false;
        }

        // Compare property values
        Person other = (Person)obj;
        return FirstName == other.FirstName && LastName == other.LastName;
    }

    // It's recommended to also override GetHashCode() when overriding Equals()
    public override int GetHashCode()
    {
        return (FirstName, LastName).GetHashCode();
    }
}

In this example, we override the Equals() method to first check if the object being compared is null or of a different type. If either condition is met, the method returns false. Then, we cast the object to the Person type and compare the FirstName and LastName properties of both objects. If the properties match, the method returns true.

Using the Equals() method:

Now that we have overridden the Equals() method, we can use it to compare two Person objects based on their property values:

using System;

namespace EqualsTutorial
{
    class Program
    {
        static void Main(string[] args)
        {
            Person person1 = new Person { FirstName = "John", LastName = "Doe" };
            Person person2 = new Person { FirstName = "John", LastName = "Doe" };
            Person person3 = new Person { FirstName = "Jane", LastName = "Doe" };

            Console.WriteLine("person1 equals person2: " + person1.Equals(person2)); // true
            Console.WriteLine("person1 equals person3: " + person1.Equals(person3)); // false
        }
    }
}

In this tutorial, we covered how to use and override the Equals() method in C# to check whether two objects are equal based on their values. By overriding the Equals() method in custom classes, you can define object equality based on the object's properties or fields, rather than relying on the default reference equality.

C# Equals method example:

Description: The Equals method in C# is used to compare the equality of two objects.

Code:

using System;

class Program
{
    static void Main()
    {
        string str1 = "Hello";
        string str2 = "Hello";

        bool areEqual = str1.Equals(str2);
        Console.WriteLine($"Are strings equal: {areEqual}");
    }
}

C# object equality comparison:

Description: The default Equals method in C# compares object references for equality.

Code:

using System;

class Program
{
    static void Main()
    {
        object obj1 = new object();
        object obj2 = obj1;

        bool areEqual = obj1.Equals(obj2);
        Console.WriteLine($"Are objects equal: {areEqual}");
    }
}

C# override Equals method:

Description: You can override the Equals method in your custom classes to provide a meaningful equality comparison.

Code:

using System;

class Person
{
    public string Name { get; set; }

    public override bool Equals(object obj)
    {
        if (obj is Person otherPerson)
        {
            return Name == otherPerson.Name;
        }
        return false;
    }
}

class Program
{
    static void Main()
    {
        Person person1 = new Person { Name = "Alice" };
        Person person2 = new Person { Name = "Alice" };

        bool areEqual = person1.Equals(person2);
        Console.WriteLine($"Are persons equal: {areEqual}");
    }
}

Implementing IEquatable in C#:

Description: Implement the IEquatable<T> interface to provide a strongly-typed Equals method.

Code:

using System;

class Person : IEquatable<Person>
{
    public string Name { get; set; }

    public bool Equals(Person other)
    {
        return other != null && Name == other.Name;
    }
}

class Program
{
    static void Main()
    {
        Person person1 = new Person { Name = "Bob" };
        Person person2 = new Person { Name = "Bob" };

        bool areEqual = person1.Equals(person2);
        Console.WriteLine($"Are persons equal: {areEqual}");
    }
}

EqualityComparer in C#:

Description: EqualityComparer<T> provides default implementations of equality comparisons for value types and can be used for custom types.

Code:

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        string str1 = "Hello";
        string str2 = "Hello";

        bool areEqual = EqualityComparer<string>.Default.Equals(str1, str2);
        Console.WriteLine($"Are strings equal: {areEqual}");
    }
}