依赖倒置原则：试图理解(Dependency inversion principle: trying to understand)

 我正在学习设计模式及其周围的事物（特别是SOLID和依赖性反转原理 ），看起来我正在失去一些东西： 
 
 遵循DIP规则，我应该能够通过不在类（ 组合 ）中创建对象，而是将对象引用/指针发送到类构造函数（ 聚合 ）来使类不那么脆弱。 但这意味着我必须在其他地方创建一个实例：因此，具有聚合的一个类越灵活，另一个类就越脆弱。 
 
 请解释一下我错在哪里。 

I'm learning design patterns and things around it (like SOLID and Dependency inversion principle in particular) and it looks like I'm loosing something:
 
Following the DIP rule I should be able to make classes less fragile by not creating an object in the class (composition) but sending the object reference/pointer to the class constructor (aggregation). But this means that I have to make an instance somewhere else: so the more flexible one class with aggregation is, the more fragile the other.
 
Please explain me where am I wrong.

原文：https://stackoverflow.com/questions/28706226