Illustration of Object creation and member management styles
There are two conflicting requirements in object creation: the need for Objects never to exist in incoherent states and the need for them to be testable.
Doing work in the constructor, such as creating other objects, ensures that the object is not in an incoherent state but it means that the object is more difficult to test as the creation of required objects is hidden and is forced onto clients and mocks.
The functional style with dependency injection ensures that objects are always coherent and that they are testable.