IoC is a design principle where the control of creating and wiring objects is handed over from the application code to an external container, inverting the traditional flow where a class constructs and manages its own dependencies. Instead of `new`-ing up collaborators itself, a class simply declares what it needs and the container supplies it.

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#IoC

Why 'Inversion' Is the Right Word

The control being inverted isn't just object creation — it's the direction of the dependency lookup. A class no longer asks 'where do I get my dependency from?' (it would have to know a factory or a global registry); it just declares a need (a constructor parameter, a field) and control over satisfying that need is inverted onto the container. This is what makes classes testable in isolation — you can hand them mocks instead.

Traditional: object creates its own dependencies · IoC: container creates and hands them in

Interview Answer

IoC means an external container, not the object itself, is responsible for creating and injecting an object's dependencies. Dependency Injection is the specific pattern Spring uses to implement IoC — the container reads your bean definitions, constructs objects in dependency order, and pushes collaborators in via constructors or setters instead of the object pulling them in itself.