StringBuffer vs StringBuidler算是面试中露脸频率非常高的两兄弟

A mutable sequence of characters. This class provides an API compatible

• with StringBuffer, but with no guarantee of synchronization. This class is designed for use as a drop-in replacement for $StringBuffer$ in places where the string buffer was being used by a single thread (as is generally the case). Where possible, it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.