依赖注入和控制反转
问题描述：
依赖关系的具体实现是什么意思？
what does " concrete implementations of the dependencies" means?
答
依赖的具体实现意味着针对具体类而不是接口进行编程。所以依赖类更加紧密耦合。所以应该考虑使用接口来避免这种耦合。
依赖注入和控制反转的良好读数
关于依赖倒置原理，控制和依赖倒置的绝对初学者教程注入 [ ^ ]
希望这会有所帮助......
A concrete implementation of dependency means programming against a concrete class instead of interface. So the dependency classes are more tightly coupled. So should consider use interface to avoid this coupling.
A good read for Dependency injection and inversion of control
An Absolute Beginner's Tutorial on Dependency Inversion Principle, Inversion of Control and Dependency Injection[^]
Hope this helps...