# Constructor Injection

*noun*

say it: **“kun-STRUK-ter in-JEK-shun”** **/kənˈstrʌktər ɪnˈdʒɛkʃən/**

A class taking the objects it needs as constructor parameters instead of creating them itself.

## What is **Constructor Injection**?

**Constructor Injection** — A class lists the objects it needs as constructor parameters and keeps them, instead of creating them with `new`. Whoever creates the class decides which ones to pass: the real email sender in the app, a fake one in a test.

```csharp
class OrderService
{
    private readonly IEmailSender email;
    public OrderService(IEmailSender email) => this.email = email;
    public void Place(Order order) => email.Send(order.CustomerEmail, "Thanks!");
}
```

## In a sentence

- “With **constructor injection**, OrderService gets its email sender from whoever creates it.”

Level: Journeyman · [More OOP terms at this level](https://www.ask-codey.com/glossary?category=oop&level=3)

Updated: October 28, 2026

Source: https://www.ask-codey.com/glossary/constructor-injection-oop