我试图转换一个无符号的有符号字节。问题是我接收的数据是无符号的,Java不支持无符号字节,所以当它读取数据时,它将其视为有符号的。
我尝试通过下面的解决方案转换它,我从Stack Overflow。
public static int unsignedToBytes(byte a)
{
int b = a & 0xFF;
return b;
}
但是当它再次以字节为单位转换时,我得到了相同的带符号数据。我试图使用此数据作为参数的Java函数,只接受一个字节作为参数,所以我不能使用任何其他数据类型。我该如何解决这个问题?
在Java中使用unsigned字节的完整指南:
Java中的无符号字节
(答案来源)
Java语言不提供任何类似unsigned关键字的东西。根据语言规范,一个字节表示−128 - 127之间的值。例如,如果将一个字节转换为int类型,Java将把第一位解释为符号并使用符号扩展。
也就是说,没有什么可以阻止您将一个字节简单地视为8位,并将这些位解释为0到255之间的值。只要记住,你不能把你的解释强加给别人的方法。如果一个方法接受一个字节,那么该方法接受−128到127之间的值,除非另有明确说明。
下面是一些有用的转换/操作,方便您使用:
从int到int的转换
// From int to unsigned byte
int i = 200; // some value between 0 and 255
byte b = (byte) i; // 8 bits representing that value
// From unsigned byte to int
byte b = 123; // 8 bits representing a value between 0 and 255
int i = b & 0xFF; // an int representing the same value
(或者,如果你使用的是Java 8+,使用Byte.toUnsignedInt。)
解析/格式化
最好的方法是使用上面的转换:
// Parse an unsigned byte
byte b = (byte) Integer.parseInt("200");
// Print an unsigned byte
System.out.println("Value of my unsigned byte: " + (b & 0xFF));
算法
2补表示“只适用于”加法、减法和乘法:
// two unsigned bytes
byte b1 = (byte) 200;
byte b2 = (byte) 15;
byte sum = (byte) (b1 + b2); // 215
byte diff = (byte) (b1 - b2); // 185
byte prod = (byte) (b2 * b2); // 225
除法需要手动转换操作数:
byte ratio = (byte) ((b1 & 0xFF) / (b2 & 0xFF));
我试图使用此数据作为参数的Java函数,只接受一个字节作为参数
这与函数接受一个大于2^32-1的整数并没有本质上的区别。
这听起来似乎取决于函数是如何定义和记录的;我认为有三种可能:
It may explicitly document that the function treats the byte as an unsigned value, in which case the function probably should do what you expect but would seem to be implemented wrong. For the integer case, the function would probably declare the parameter as an unsigned integer, but that is not possible for the byte case.
It may document that the value for this argument must be greater than (or perhaps equal to) zero, in which case you are misusing the function (passing an out-of-range parameter), expecting it to do more than it was designed to do. With some level of debugging support you might expect the function to throw an exception or fail an assertion.
The documentation may say nothing, in which case a negative parameter is, well, a negative parameter and whether that has any meaning depends on what the function does. If this is meaningless then perhaps the function should really be defined/documented as (2). If this is meaningful in an nonobvious manner (e.g. non-negative values are used to index into an array, and negative values are used to index back from the end of the array so -1 means the last element) the documentation should say what it means and I would expect that it isn't what you want it to do anyway.