方法局部内部类不能使用方法内声明的变量 [英] method-local inner class cannot use variables declared within the method

问题描述

为什么局部于方法内部的类不能使用在封闭方法内部声明的变量，除了标记为final的那些变量外，我知道在内部类实例保持有效的同时，在封闭方法内部声明的变量可能会消失，但是当这个变量声明为最终变量?

Why a method-local inner class can't use variables declared inside the enclosing method except those marked final, i know that the variables declared inside the enclosing method might vanishes while the inner class instance remains valid, but what has changed when this variable/s is declared final?

推荐答案

原因是它是在

使用但未在内部类中声明的任何局部变量，形式参数或异常参数必须声明为final.

Any local variable, formal parameter, or exception parameter used but not declared in an inner class must be declared final.

还要注意，项目lambda(java 8)旨在引入java中的闭包(以替换匿名类)，引入了有效final的概念，该概念将允许您在lambda表达式中使用非final变量，只要您无需在闭包内进行修改.

Also note that project lambda (java 8), which aims at introducing closures in java (to replace anonymous classes), introduces the notion of effectively final which will allow you to use a non final variable within a lambda expression as long as you don't modify it within the closure.

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