C#
The Object class
Learn Object, the ancestor of all classes, and ToString, Equals, GetHashCode.
The Object root class
In C# every class implicitly inherits from object (System.Object). You do not write : object; the compiler adds it automatically. That is why every object has ToString, Equals and GetHashCode methods.
An object reference can hold any object: object o = new Book(); is valid. With boxing you can also assign value types to object: object box = 42;.
ToString override
The default ToString returns the class name, which is often useless. In your own class you override it to produce a meaningful string: public override string ToString() { return Name + " - " + Age; }.
Then Console.WriteLine(person) automatically calls ToString and gives useful output. This is the most frequently overridden method for debugging and logging. Always return a meaningful, short representation.
Exercise Override ToString in the Person class
Define a Person class with public string Name { get; set; } and public int Age { get; set; } properties. Then add a public override string ToString() method with return Name + " - " + Age; in the body. Inside Main create an instance with new Person { Name = "Alex", Age = 30 } and print it with Console.WriteLine(person).
Show example solution
Add Name and Age properties to Person. Write ToString override with return Name + " - " + Age;. In Main write Person p = new Person { Name = "Alex", Age = 30 }; Console.WriteLine(p);
Example solution:
using System;
class Person
{
public string Name { get; set; }
public int Age { get; set; }
public override string ToString()
{
return Name + " - " + Age;
}
}
class Program
{
static void Main()
{
Person p = new Person { Name = "Alex", Age = 30 };
Console.WriteLine(p);
}
}
Test yourself
-
Match each Object method to its purpose
- ToString
- Text representation
- Equals
- Equality check
- GetHashCode
- Hash code
- GetType
- Type info
-
What class does every class inherit from?
Show answer
object — Correct. Every class inherits from object.
-
Complete the ToString override
public override string ____() { return Name; }
Show answer
public override string ToString() { return Name; }
Next lesson: Summary - Inheritance
