System.out.println(4 * 2147483647)在Java中如何等于-4? [英] How is System.out.println(4*2147483647) equal to -4 in java?

问题描述

我是Java初学者，对此颇为困惑.

I am a Java beginner and pretty confused with this.

System.out.println(4 * 2147483647)在Java中如何等于-4?

How is System.out.println(4*2147483647) equal to -4 in java?

推荐答案

这是由于整数静默溢出造成的.

It is due to integer silent overflow.

2147483647 == Integer.MAX_VALUE 是整数的最大值.

严重溢出意味着 2147483647 + 1 == Integer.MIN_VALUE = -2147483648
然后您可以看到 2147483647 + 2147483647 == 2147483647 +(-2147483648 +1-== -2

换句话说， 2147483647 * 2 == -2 ，现在您可以了解为什么 2147483647 * 4 == -4 .

In other words, 2147483647 * 2 == -2, and you can now see why 2147483647 * 4 == -4.

从技术上讲，结果由定义Java语言规范#15.17.1 :

如果整数乘法溢出，则结果是数学乘积的低阶位，以某种足够大的二进制补码格式表示.结果，如果发生溢出，则结果的符号可能与两个操作数值的数学乘积的符号不同.

If an integer multiplication overflows, then the result is the low-order bits of the mathematical product as represented in some sufficiently large two's-complement format. As a result, if overflow occurs, then the sign of the result may not be the same as the sign of the mathematical product of the two operand values.

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