Java - 操作顺序 - 在一行中使用两个赋值运算符 [英] Java - Order of Operations - Using Two Assignment Operators in a Single Line

问题描述

在一行中使用两个赋值运算符时的操作顺序是什么?

What are the order of operations when using two assignment operators in a single line?

public static void main(String[] args){
    int i = 0;
    int[] a = {3, 6};
    a[i] = i = 9; // this line in particular
    System.out.println(i + " " + a[0] + " " + a[1]);
}

感谢您的帖子.我知道 = 从右边取值，但是当我编译它时，我得到:

Thanks for the posts. I get that = takes values from the right, but when I compile this I get:

9 9 6

我认为它会是 ArrayOutOfBounds 异常，但它正在分配 'a[i]' 之前它正在移动到 9.它只是为数组这样做吗?

I thought it would have been and ArrayOutOfBounds exception, but it is assigning 'a[i]' before it's moving over the 9. Does it just do that for arrays?

推荐答案

= 被解析为右结合，但求值顺序是从左到右.

= is parsed as right-associative, but order of evaluation is left-to-right.

所以:语句被解析为a[i] = (i = 9).然而，当 i 仍然是 0.

So: The statement is parsed as a[i] = (i = 9). However, the expression i in a[i] is evaluated before the right hand side (i = 9), when i is still 0.

这相当于:

int[] #0 = a;
int #1 = i;
int #2 = 9;
i = #2;
#0[#1] = #2;

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