juniorDependency Injection
What is Constructor Injection?
Updated Apr 28, 2026
Short answer
Constructor Injection is the process of providing dependencies to a class through its constructor when the class is instantiated.
Deep explanation
It is the most common and recommended form of DI. It guarantees that the class is fully initialized with all required dependencies before it can be used, preventing null reference exceptions and promoting immutable state.
Real-world example
Requiring a database connection string to be passed when a data access class is created.
Common mistakes
- Having too many parameters in the constructor (constructor over-injection), indicating a violation of the Single Responsibility Principle.
Follow-up questions
- When should you NOT use constructor injection?