最终变量在jshell中运行不正常 [英] final variables are not functioning well in jshell

问题描述

我正在使用JDK9的jshell。

我刚刚创建了一个最终变量并为其分配了一个值。
在下一行中，我刚刚修改了值。令我惊讶的是，修改最终变量时没有错误。

以下是代码段：

  jshell>最终整数r = 0; 
 |警告：
 | 
 |顶级声明中不允许使用修饰符 final最终整数r = 0; 
 | ^ --- ^ 
 r ==> 0 
 
 jshell> r = 1； 
 r ==> 1 
 
 jshell> System.out.println（ r = + r）
r = 1 
  

是jshell会带来什么？还是有其他方法可以在jshell中使用最终变量？

解决方案

在顶层创建最终变量的同时不应该练习。但是我想并没有限制这种用法的硬方法。

来自

I am working with jshell of JDK9.

I just created a final variable and assigned a value to it. And in the next line i just modified the value. And to my surprise, there was no error when modifying the final variables.

Here is the code snippets:

jshell> final int r = 0;
|  Warning:
|  Modifier 'final'  not permitted in top-level declarations, ignored
|  final int r = 0;
|  ^---^
r ==> 0

jshell> r = 1;
r ==> 1

jshell> System.out.println("r = "+r)
r = 1

Is it what is expected from jshell? or there is some other way to work with final variables in jshell?

解决方案

While creating a final variable at the top-level is not supposed to be practiced. But I guess there is no hard way of restricting such usages.

From the documentation around JShell.eval

The modifiers public, protected, private, static, and final are not allowed on op-level declarations and are ignored with a warning.

Synchronized, native, abstract, and default top-level methods are not allowed and are errors.

If a previous definition of a declaration is overwritten then there will be an event showing its status changed to OVERWRITTEN, this will not occur for dropped, rejected, or already overwritten declarations.

The warning stated above is quite visible when you execute jshell in verbose mode as follows:

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