因为 StringBuffer 是可变的，其主要用途是构建字符串。如果你想比较内容，请调用 StringBuffer＃toString（）并比较返回的值。

Because StringBuffer is mutable, and its primary use is for constructing strings. If you want to compare content, call StringBuffer#toString() and compare the returned value.

它不是通常用于覆盖 hashCode（）的可变对象，因为修改了这个用作 HashMap中的键的对象可能导致存储的值丢失。

It is not generally useful to override hashCode() for mutable objects, since modifying such an object that is used as a key in a HashMap could cause the stored value to be "lost."