java - 为什么java语句评估会发生这样的情况？

Question

int z = 1;
System.out.println(z++ == ++z);
System.out.println(++z == z++);

输出将是:

false
true

我不明白为什么，请向我解释一下。

Answer 1

Operands of == are evaluated left to right ，并且 ++ 具有更高的优先级，因此您的代码相当于:

int z = 1;
int tmp1 = z++; //tmp1 = 1 / z = 2
int tmp2 = ++z; //tmp2 = 3 / z = 3
System.out.println(tmp1 == tmp2);

tmp1 = ++z; //tmp1 = 4 / z = 4
tmp2 = z++; //tmp2 = 4 / z = 5
System.out.println(tmp1 == tmp2);

我假设您了解 z++ 和 ++z 之间的区别:

• tmp1 = z++; 可以分解为:tmp1 = z; z = z + 1;
• 而tmp2 =++z;可以分解为:z = z + 1; tmp2 = z;