在Java中，为什么需要将闭包变量声明为final? [英] in java, why do closured variables need to be declared final?

问题描述

final Object o;

List l = new ArrayList(){{
    // closure over o, in lexical scope
    this.add(o);
}};

为什么必须将o声明为final?为什么其他具有可变vars的JVM语言没有这个要求?

why must o be declared final? why don't other JVM languages with mutable vars have this requirement?

推荐答案

这不是对JVM的深入了解，所有这些都发生在语法糖级别.原因是通过闭包导出非最终变量使其容易受到数据争用问题的影响，并且由于Java被设计为蓝领"语言，因此本来温和安全的本地变量的行为发生了令人惊讶的变化被认为太高级"了.

This is not JVM-deep, it all happens at syntactic-sugar level. The reason is that exporting a non-final var via a closure makes it vulnerable to datarace issues and, since Java was designed to be a "blue-collar" language, such a surprising change in the behavior of an otherwise tame and safe local var was deemed way too "advanced".

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