检查java中是否已经定义了一个变量 [英] Check if a variable is already defined in java

问题描述

到达那里时，我需要检查变量是否已经在代码中的其他地方定义了.

I need to check if a variable is already defined somewhere else in the code when getting there.

由于JSP中包含了某些内容，因此有时会在两个地方定义一个变量，然后Java返回一个错误.使用jsp:include似乎也不起作用.

Because of includes in JSP, I sometimes get a variable defined in two spots, and java then returns an error. Using the jsp:include doesn't seem to work either.

我正在寻找c的#ifndef形式的内容，而不是在预处理器中(因为这是java)，以避免重复的局部变量问题.

I am looking for something in the form of an #ifndef of c, but not in the pre-processor (as this is java) to avoid having a duplicate local variable issue.

有时我不能使用==null或isnull()，根本就不会定义变量，而不仅仅是未初始化

I cannot use ==null or isnull() as sometimes, the variable won't be defined at all, not just uninitialized

推荐答案

我不认为有什么魔术可以解决您的问题，唯一可以做的就是在jsp中应用命名约定文件，尤其是那些打算包含在内的文件.例如，您可以在变量名称前添加前缀，假设您的文件为myfolder/foo.jsp，变量为bar，则可以将其重命名为myfolder_foo_jsp_bar，这样就不会再有任何命名冲突了.

I don't believe that there is a magic trick that will solve your issue, the only thing that could be done is to apply a naming convention in your jsp files especially those which are meant to be included. You can for example add a prefix to the name of your variables, assuming that your file is myfolder/foo.jsp and your variable is bar, you can rename it to myfolder_foo_jsp_bar this way you won't have any naming collision anymore.

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