Java Integers Min_Value 负数然后比较
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Java Integers Min_Value negative then compare
提问by Quinma
I have a test tomorrow and I cant understand my books explanation, I appreciate the help:
我明天有考试，我无法理解我的书籍解释，我很感激帮助：
public class TestClass{
public static void main(String[] args) throws Exception{
int a = Integer.MIN_VALUE;
int b = -a;
System.out.println( a+ " "+b);
}
}
Output: -2147483648 -2147483648
输出： -2147483648 -2147483648
Why does this print 2 negative numbers of the same magnitude and not a positive and negative?
为什么这会打印 2 个大小相同的负数而不是正数和负数？
回答by assylias
Because of silent integer overflow: Integer.MIN_VALUEis -2^31and Integer.MAX_VALUEis 2^31-1, so -Integer.MIN_VALUEis 2^31, which is Integer.MAX_VALUE + 1, which by definition is too large for an integer. So it overflows and becomes Integer.MIN_VALUE...
由于无声整数溢出：Integer.MIN_VALUEis-2^31和Integer.MAX_VALUEis 2^31-1，所以-Integer.MIN_VALUEis 2^31， which is Integer.MAX_VALUE + 1，根据定义，对于整数来说太大了。所以它溢出并变成Integer.MIN_VALUE......
You can also check that:
您还可以检查：
System.out.println(Integer.MAX_VALUE + 1);
prints the same thing.
打印同样的东西。
More technically, the result is defined by the Java Language Specification #15.18.2:
从技术上讲，结果由Java 语言规范 #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.
如果整数加法溢出，则结果是数学和的低位，以某种足够大的二进制补码格式表示。如果发生溢出，则结果的符号与两个操作数值的数学和的符号不同。
回答by Jo?o Mendes
Basically, because Integer.MAX_VALUEis actually only 2147483647, so -Integer.MIN_VALUE, which would be +2147483648, actually overflows the capacity of the internal binary representation of integers. Thus, the result "loops around" back to Integer.MIN_VALUE, or -2147483648.
基本上，因为Integer.MAX_VALUE实际上只有 2147483647，所以-Integer.MIN_VALUE，即 +2147483648，实际上溢出了整数内部二进制表示的容量。因此，结果“循环”回到Integer.MIN_VALUE, 或 -2147483648。
If you did long b = -((long)a);instead, you would get the expected result.
如果你这样做了long b = -((long)a);，你会得到预期的结果。
回答by user2332921
To show this even more clearly:
为了更清楚地表明这一点：
<br>
Integer.MIN_VALUE is -2^31 = -2147483648<br>
Integer.MAX_VALUE is 2^31-1 = 2147483647
/*notice this is 1 less than the negative value above*/
<br>
1Integer.MAX_VALUEcan not take 2147483648. This is too large number for Integer by exactly 1. This causes the number to go back on the scale from max value back to starting poing which is the min value.
1Integer.MAX_VALUE不能拿2147483648。这对于整数来说太大了，正好是 1。这会导致数字从最大值回到起始点，这是最小值。
