0x80000000 在java中如何等同于-2147483648？
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How is 0x80000000 equated to -2147483648 in java?
提问by vikkyhacks
Taking the binary of 0x80000000we get
取二进制0x80000000我们得到
1000 0000 0000 0000 0000 0000 0000 0000
How does this equate to -2147483648. I got this question with this program.
这如何等同于-2147483648. 我在这个程序中遇到了这个问题。
class a
{
public static void main(String[] args)
{
int a = 0x80000000;
System.out.printf("%x %d\n",a,a);
}
}
meow@VikkyHacks:~/Arena/java$ java a
80000000 -2147483648
EDITI learned that 2's complement is used to represent negative numbers. When I try to equate this with that 1's complement would be
编辑我了解到 2 的补码用于表示负数。当我试图将其与 1 的补码相提并论时
1's Comp. :: 0111 1111 1111 1111 1111 1111 1111 1111
2's Comp. :: 1000 0000 0000 0000 0000 0000 0000 0000
which again does not make any sense, How does 0x80000000equate to -2147483648
这又没有任何意义，如何0x80000000等同于-2147483648
采纳答案by Jon Skeet
This is what happens with signed integer overflow, basically.
基本上，这就是有符号整数溢出会发生的情况。
It's simpler to take byteas an example. A bytevalue is always in the range -128 to 127 (inclusive). So if you have a value of 127(which is 0x7f) if you add 1, you get -128. That's also what you get if you cast 128 (0x80) to byte:
byte举个例子就更简单了。甲byte值始终是在-128到127（含）的范围内。所以如果你有一个值127（即 0x7f），如果你加 1，你会得到 -128。如果您将 128 (0x80) 转换为byte：
int x = 0x80; // 128
byte y = (byte) x; // -128
Overflow (in 2s complement integer representations) always goes from the highest expressible number to the lowest one.
溢出（在 2s 补码整数表示中）总是从最高的可表达数到最低的数。
For unsignedtypes, the highest value overflows to 0 (which is again the lowest expressible number). This is harder to show in Java as the only unsigned type is char:
对于无符号类型，最高值溢出到 0（这也是最低的可表示数）。这在 Java 中更难显示，因为唯一的无符号类型是char：
char x = (char) 0xffff;
x++;
System.out.println((int) x); // 0
回答by N. Pamnani
This is the case when there is overflow, with respect to the range of a data type. Here is an example that I can share.
就数据类型的范围而言，出现溢出时就是这种情况。这是我可以分享的一个例子。
int number = 0x80; // 0x80 is hexadecimal for 128 (decimal)
byte castedNumber = (byte)(number); // On casting, there is overflow,as byte ranges from -128 to 127 (inclusive).
System.out.println(castedNumber); //Output is -128.
