为什么这个语句不适用于java x ^ = y ^ = x ^ = y; [英] Why is this statement not working in java x ^= y ^= x ^= y;

问题描述

int x=1;
int y=2;
x ^= y ^= x ^= y;

我期待交换价值。但它给出x = 0和y = 1。
当我尝试用C语言时，它给出了正确的结果。

I am expecting the values to be swapped.But it gives x=0 and y=1. when i tried in C language it gives the correct result.

推荐答案

你的陈述大致相当于这个扩展的形式：

Your statement is roughly equivalent to this expanded form:

x = x ^ (y = y ^ (x = x ^ y));

与C不同，在Java中，二进制运算符的左操作数保证在右边之前进行求值操作数。评估如下：

Unlike in C, in Java the left operand of a binary operator is guaranteed to be evaluated before the right operand. Evaluation occurs as follows:

x = x ^ (y = y ^ (x = x ^ y))
x = 1 ^ (y = 2 ^ (x = 1 ^ 2))
x = 1 ^ (y = 2 ^ (x = 3))
x = 1 ^ (y = 2 ^ 3)             // x is set to 3 
x = 1 ^ (y = 1)
x = 1 ^ 1                       // y is set to 1
x = 0                           // x is set to 0

您可以反转每个xor表达式的参数顺序，以便在再次计算变量之前完成赋值： / p>

You could reverse the order of the arguments to each xor expression so that the assignment is done before the variable is evaluated again:

x = (y = (x = x ^ y) ^ y) ^ x
x = (y = (x = 1 ^ 2) ^ y) ^ x
x = (y = (x = 3) ^ y) ^ x 
x = (y = 3 ^ y) ^ x             // x is set to 3
x = (y = 3 ^ 2) ^ x
x = (y = 1) ^ x
x = 1 ^ x                       // y is set to 1
x = 1 ^ 3
x = 2                           // x is set to 2

这是一个更紧凑的版本，也适用：

This is a more compact version that also works:

x = (y ^= x ^= y) ^ x;

但这是交换两个变量的真正可怕方式。使用临时变量是一个更好的主意。

But this is a truly horrible way to swap two variables. It's a much better idea to use a temporary variable.

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