For DI to work, you must have an interface whose concrete class you can inject into the consumer of the behavior you desire.

为了让DI工作，必须拥有一个接口，可以把这个接口的具体类注入到需要的行为的消费者中。

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Many proponents of DI prefer constructor injection, because it means that the injected class never exists in a state where its dependencies aren't present.

许多 DI 的支持者愿意采用构造函数注入，因为这意味着注入的类永远不会出现依赖项不存在的情况。

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With DI, you can allow the container to inject the appropriate customer class either by configuring the container or implementing the injection in the code.

使用DI，可以通过配置容器或在代码中实现注入，让容器注入适合的客户类。

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