为什么“Lambda 表达式中使用的变量必须是最终的或有效的最终"?忽略实例变量的警告

问题描述

I'm studying java 8 streams and the only problem I have is understanding lambdas is why the effectively final warning in lambdas is ignored for instance(and static) variables. I can't seem to find any reference to it online, as most pages will just talk about the definition of being "effectively final".

public class LambdaTest {

    int instanceCounter = 0;

    public void method() {
        int localCounter = 0;
        instanceCounter = 5; //Re-assign instance counter so it is no longer effectively final

        Stream.of(1,2,3).forEach(elem -> instanceCounter++); //WHY DOES THE COMPILER NOT COMPLAIN HERE
        Stream.of(1,2,3).forEach(elem -> localCounter++); //Does not compile because localCounter is not effectively final
    }
}

解决方案

We tend to forget that instanceCounter is actually this.instanceCounter, you are capturing this which is well, effectively final. As to why this is needed, the answer is obviously here

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