Java中的最终变量操作 [英] Final variable manipulation in Java

问题描述

有人可以告诉我在Java的上下文中以下行的含义是什么：

Could anyone please tell me what is the meaning of the following line in context of Java:

最终变量仍然可以是
操纵，除非它是不可变的

final variable can still be manipulated unless it's immutable

据我所知，通过将任何变量声明为final，你不能再改变它，然后他们在上面的行中用不可变这个词是什么意思？

As far as I know, by declaring any variable as final, you can't change it again, then what they mean with the word immutable in above line?

推荐答案

这意味着如果你的最终变量是一个引用类型（即不是像int这样的原语），那么它只是无法更改的引用。它不能被引用到不同的对象，但是如果类允许的话，它所引用的对象的字段仍然可以被改变。例如：

It means that if your final variable is a reference type (i.e. not a primitive like int), then it's only the reference that cannot be changed. It cannot be made to refer to a different object, but the fields of the object it refers to can still be changed, if the class allows it. For example:

final StringBuffer s = new StringBuffer();

StringBuffer的内容仍然可以随意更改：

The content of the StringBuffer can still be changed arbitrarily:

s.append("something");

但你不能说：

s = null;

或

s = anotherBuffer;

另一方面：

final String s = "";

字符串是不可变的 - 根本没有任何方法可以让你更改字符串（除非你使用反射 - 然后去地狱）。

Strings are immutable - there simply isn't any method that would enable you to change a String (unless you use Reflection - and go to hell).

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