Understanding the need for a DI framework

Question

This might be a naive question. I\'m currently learning the Spring framework and dependency injection. While the basic principle of DI is rather easy to grasp, it\'s

Answer 1

One of the biggest benefits of using Dependency Injection is that it makes it much easier to provide mocks or stubs of a class's dependencies when creating a unit test for that class. This allows you to test the class in isolation without depending on its collaborators.

In your example, there is no way to mock or stub out Saw or SawMill in the class that where those are being instantiated. If Saw and SawMill were set via setters or the constructor, then you could pass in your own mock Saw and mock SawMill when running the unit test.