The Object Class in C#

The Object class is the base class of all classes in C# and the .NET Framework. Every class in C# implicitly inherits from the Object class, which means all objects have access to the fundamental methods provided by this base class.

When you create any class in C#, it automatically inherits from Object even if you don't explicitly specify it. This provides a common set of methods that every object can use.

Syntax

Every class implicitly inherits from Object −

public class MyClass {
   // This class inherits from Object automatically
}

// Equivalent to:
public class MyClass : Object {
   // Explicitly inheriting from Object
}

Object Class Methods

The Object class provides the following essential methods that every C# object inherits −

Using Object Class Methods

Example

using System;

public class Student {
    public string Name { get; set; }
    public int Age { get; set; }

    public Student(string name, int age) {
        Name = name;
        Age = age;
    }

    public override string ToString() {
        return $"Student: {Name}, Age: {Age}";
    }

    public override bool Equals(object obj) {
        if (obj is Student other) {
            return Name == other.Name && Age == other.Age;
        }
        return false;
    }

    public override int GetHashCode() {
        return Name.GetHashCode() ^ Age.GetHashCode();
    }
}

public class Program {
    public static void Main() {
        Student s1 = new Student("John", 20);
        Student s2 = new Student("John", 20);
        Student s3 = s1;

        Console.WriteLine("ToString(): " + s1.ToString());
        Console.WriteLine("GetType(): " + s1.GetType());
        Console.WriteLine("GetHashCode(): " + s1.GetHashCode());
        
        Console.WriteLine("s1.Equals(s2): " + s1.Equals(s2));
        Console.WriteLine("ReferenceEquals(s1, s2): " + Object.ReferenceEquals(s1, s2));
        Console.WriteLine("ReferenceEquals(s1, s3): " + Object.ReferenceEquals(s1, s3));
    }
}

The output of the above code is −

ToString(): Student: John, Age: 20
GetType(): Student
GetHashCode(): 1248104350
s1.Equals(s2): True
ReferenceEquals(s1, s2): False
ReferenceEquals(s1, s3): True

Commonly Overridden Methods

Example

using System;

public class Product {
    public string Name { get; set; }
    public decimal Price { get; set; }

    public Product(string name, decimal price) {
        Name = name;
        Price = price;
    }

    // Override ToString() for meaningful string representation
    public override string ToString() {
        return $"{Name} - ${Price:F2}";
    }

    // Override Equals() for value-based comparison
    public override bool Equals(object obj) {
        return obj is Product product && 
               Name == product.Name && 
               Price == product.Price;
    }

    // Override GetHashCode() when overriding Equals()
    public override int GetHashCode() {
        return HashCode.Combine(Name, Price);
    }
}

public class Program {
    public static void Main() {
        Product p1 = new Product("Laptop", 999.99m);
        Product p2 = new Product("Laptop", 999.99m);

        Console.WriteLine("Product 1: " + p1);
        Console.WriteLine("Product 2: " + p2);
        Console.WriteLine("Are they equal? " + p1.Equals(p2));
        Console.WriteLine("Same reference? " + ReferenceEquals(p1, p2));
    }
}

The output of the above code is −

Product 1: Laptop - $999.99
Product 2: Laptop - $999.99
Are they equal? True
Same reference? False

Object as Universal Type

Example

using System;

public class Program {
    public static void PrintObject(object obj) {
        Console.WriteLine("Type: " + obj.GetType().Name);
        Console.WriteLine("Value: " + obj.ToString());
        Console.WriteLine("Hash: " + obj.GetHashCode());
        Console.WriteLine("---");
    }

    public static void Main() {
        PrintObject(42);
        PrintObject("Hello World");
        PrintObject(true);
        PrintObject(new DateTime(2024, 1, 15));
    }
}

The output of the above code is −

Type: Int32
Value: 42
Hash: 42
---
Type: String
Value: Hello World
Hash: -1989457895
---
Type: Boolean
Value: True
Hash: 1
---
Type: DateTime
Value: 1/15/2024 12:00:00 AM
Hash: -1948092588
---

Conclusion

The Object class is the root of the C# type hierarchy, providing essential methods like ToString(), Equals(), and GetHashCode() that every object inherits. Understanding and properly overriding these methods is crucial for creating well-behaved custom classes that integrate seamlessly with the .NET Framework.