Clients should find no surprises when receiving a final invoice, but if the consultant neglects to include shipping costs in preliminary conversations, such fees will prove problematic.
当收到最终发货单的时候，客户应当不会有出乎意料的发现，但是如果顾问疏忽大意，没有在初步沟通中将运输成本考虑在内，此类费用就会是个问题。
It defines a set of method names and their argument signatures, but no implementations. The invoice example might look like Listing 1.
它定义了一组方法名称和其参数签名，但是没有实现。
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