If you don't extend a parent class, the default parent is AnyRef, a direct child class of Any.

如果你不继承任何父类，默认的父亲是AnyRef, Any的一个直接子类。

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We discuss the difference between Any and AnyRef when we discuss the Scala type hierarchy in the section called "the Scala type hierarchy".

我们会在“scala类型层级结构”章节中讨论Any和AnyRef的区别。

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