Java Integer.MIN_VALUE 的负数然后比较产生两个负数

Question

我明天要考试，我看不懂我书上的解释，感谢帮助:

public class TestClass{
      public static void main(String[] args) throws Exception{
            int a = Integer.MIN_VALUE;
            int b = -a;
            System.out.println( a+ "   "+b);
      }
}

输出:-2147483648 -2147483648

为什么这会打印出 2 个大小相同的负数而不是正数和负数？

Answer 1

由于静默整数溢出:Integer.MIN_VALUE 是 -2^31 而 Integer.MAX_VALUE 是 2^31- 1，所以-Integer.MIN_VALUE是2^31，也就是Integer.MAX_VALUE + 1，根据定义也是对于整数来说很大。所以它溢出并变成Integer.MIN_VALUE...

您还可以检查:

System.out.println(Integer.MAX_VALUE + 1);

打印同样的东西。

从技术上讲，结果由 Java Language Specification #15.18.2 定义:

If an integer addition overflows, then the result is the low-order bits of the mathematical sum as represented in some sufficiently large two's-complement format. If overflow occurs, then the sign of the result is not the same as the sign of the mathematical sum of the two operand values.