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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