What is Dependency Injection in Spring?

Dependency Injection (DI) is the specific technique Spring uses to implement IoC: rather than a bean looking up or constructing the objects it needs, the container "injects" those dependencies into it, usually through a constructor, a setter, or a field.

For example, an OrderService that needs a PaymentGateway simply declares a constructor parameter of that type; Spring resolves a matching bean and passes it in automatically. This keeps classes free of wiring logic and lookup code, so the service never calls new StripeGateway() directly - it just asks for a PaymentGateway and trusts the container to supply one, which makes swapping implementations or mocking dependencies in tests straightforward.

Invest now in Acorns!!! 🚀
Join Acorns and get your $5 bonus!

Acorns is a micro-investing app that automatically invests your "spare change" from daily purchases into diversified, expert-built portfolios of ETFs. It is designed for beginners, allowing you to start investing with as little as $5. The service automates saving and investing. Disclosure: I may receive a referral bonus.

Invest now!!! Get Free equity stock (US, UK only)!

Use Robinhood app to invest in stocks. It is safe and secure. Use the Referral link to claim your free stock when you sign up!.

The Robinhood app makes it easy to trade stocks, crypto and more.

Webull! Receive free stock by signing up using the link: Webull signup.