第十三章 函数式编程 中的两处翻译错误 ，附上原文以供参考

The value of @FunctionalInterface is seen in the definition of NotFunctional: More than one method in your interface produces a compile-time error message.

Because we can simply write Function<Integer,Double> and produce working results, it’s clear that the only reason for the primitive variants of the functionals is to prevent the autoboxing and autounboxing involved with passing arguments and returning results. That is, for performance.