Generic class
Learn to define a generic class with <T>.
What is a generic class?
A generic class is declared with a type parameter. The letter T is the most common parameter name; it is a placeholder type. The declaration class Box<T> says that Box can work with any type.
When you use it, you supply a concrete type: Box<int> is an integer box, Box<string> is a string box. The compiler produces a separate type per instantiation, so type safety is preserved and boxing is avoided. Generic classes reduce code duplication while keeping safety.
Same class, different types
After defining a generic class you can instantiate it with any type. Box<int> and Box<string> are instances of the same template but with different types.
The inner T Value property changes with the concrete type: int Value in Box<int>, string Value in Box<string>. The compiler catches wrong assignments at compile time. A non-generic solution would lose this safety.
Exercise Define the Box<T> class
Define a generic Box<T> class with a public T Value { get; set; } property. In Main create a Box<int> and a Box<string>; assign 42 and "Hello" to their Values. Print each Value with Console.WriteLine.
Show example solution
Write class Box<T> { public T Value { get; set; } }. In Main add var intBox = new Box<int> { Value = 42 }; var strBox = new Box<string> { Value = "Hello" }; Console.WriteLine(intBox.Value); Console.WriteLine(strBox.Value);
Example solution:
using System;
class Box<T>
{
public T Value { get; set; }
}
class Program
{
static void Main()
{
var intBox = new Box<int> { Value = 42 };
var strBox = new Box<string> { Value = "Hello" };
Console.WriteLine(intBox.Value);
Console.WriteLine(strBox.Value);
}
}Test yourself
-
How is a Box<T> class declared?
- class Box<T> { }
- class Box<T> T { }
- class Box(T) { }
- class Box : T { }
Show answer
class Box<T> { } — Correct. The type parameter goes in angle brackets after the class name.
-
The type parameter letter
class Box<____> { public T Value { get; set; } }Show answer
class Box<T> { public T Value { get; set; } } -
Match each generic piece to its meaning
- <T>
- Type parameter
- Box<int>
- Concrete instance
- T Value
- Type-parameter property
- new Box<T>()
- Instance creation