If you only have a concrete class, you can create an interface from the class, change your application code to program to the interface, and then proceed as described above.

如果您只有一个具体的类，那么您可以从类中创建一个接口，您的应用程序代码改写为接口，然后按照前面的描述继续进行。

youdao

A class (whether abstract or concrete) that implements an interface does not really inherit anything from the interface it implements.

一个类(不管是抽象的还是具体的)实现一个接口并不真正从它实现的接口继承任何东西。

youdao

The concrete DAO class contains logic for accessing data from a specific data source.

具体的dao类包含访问特定数据源的数据的逻辑。

youdao

So he is open to new ideas, but he will not accept a proposal that has some vague promise of revenues produced from closing loopholes and limiting deductions from the wealthy that is coupled with very concrete burdens placed on the middle class and seniors.

WHITEHOUSE: The White House