英文:
Is there a way to multiply a byte type and a float type value in Java?
问题
在我的 `C++` 代码中，我有一些 `unsigned char`，如果我将值255（0xff）乘以0.5，我会得到127。但在我的Java代码中，我无法这样做，因为`byte`是有符号的。
代码示例：
byte a = (byte) 0xFF;
System.out.println(String.format("0x%02X ", a));
float b = 0.5;
float c = a * b;
System.out.println(String.format("0x%02X ", c));
结果将会是：
0xff
0x00
有没有办法让我得到 *7f*，或者在 `int` 中得到 *127*，并将该值重新存储在一个 `byte` 类型的变量中？
英文:
In C++ code i have unsigned char's and if I multiply a 255(0xff) value with 0.5 I'll get 127.But in my java code I can't do that because byte is signed.
Code example:
byte a = (byte) 0xFF;
System.out.println(String.format("0x%02X ", a));
float b = 0.5;
float c = a * b;
System.out.println(String.format("0x%02X ", c));
And the result would be
0xff
0x00
Is there a way to multiply so I get 7f , or in int 127 and store back that value in a byte type variable?
答案1
得分: 2
byte 类型在Java中是有符号的。因此，字节 0xFF 表示的是 -1 而不是 +255。所以 -1 的一半是 -0.5 ...... 当你转换回 byte 类型时，要么是 -1 要么是 0 ...... 具体取决于四舍五入。
你可能应该像这样做：
byte a = (byte) 0xFF;
float c = Byte.toUnsignedInt(a) * 0.5f;
byte d = (byte) c;
或者，你可以使用整数除法：
byte a = (byte) 0xFF;
int c = Byte.toUnsignedInt(a) / 2;
byte d = (byte) c;
... 不过这会向零截断（这些数是正数），而不是四舍五入。
英文:
The byte type is signed in Java. So the byte 0xFF represents -1 not +255. So half of -1 is -0.5 ... which when you convert back to a byte would be either -1 or 0 ... depending on rounding.
You probably should do something like this:
byte a = (byte) 0xFF;
float c = Byte.toUnsignedInt(a) * 0.5f;
byte d = (byte) c;
Alternatively, you could use integer division:
byte a = (byte) 0xFF;
int c = Byte.toUnsignedInt(a) / 2;
byte d = (byte) c;
... though that will truncate towards zero (these numbers are positive) rather than rounding.
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