final 修饰 StringBuffer 后还可以 append 吗?

可以。final 修饰的是一个引用变量,那么这个引用始终只能指向这个对象,但是这个对象内部的属性是可以变化的。

官方文档解释:once a final variable has been assigned, it always contains the same value. If a final variable holds a reference to an object, then the state of the object may be changed by operations on the object, but the variable will always refer to the same object.