[java] Java로 부호없는 바이트를 만들 수 있습니까?

프리미티브가 Java로 서명되었다는 사실은 메모리 / 전송에서 표현되는 방식과 관련이 없습니다. 바이트는 8 비트에 불과하며 서명 된 범위로 해석하는지 여부는 귀하에게 달려 있습니다. “this is signed”또는 “this is unsigned”라고 말하는 마술 깃발은 없습니다.

프리미티브가 서명되면 Java 컴파일러는 +127보다 높은 값을 바이트 (또는 -128보다 작은)에 할당하지 못하게합니다. 그러나 이것을 달성하기 위해 int (또는 short)를 다운 캐스팅하는 것을 막을 수는 없습니다.

int i = 200; // 0000 0000 0000 0000 0000 0000 1100 1000 (200)
byte b = (byte) 200; // 1100 1000 (-56 by Java specification, 200 by convention)

/*
 * Will print a negative int -56 because upcasting byte to int does
 * so called "sign extension" which yields those bits:
 * 1111 1111 1111 1111 1111 1111 1100 1000 (-56)
 *
 * But you could still choose to interpret this as +200.
 */
System.out.println(b); // "-56"

/*
 * Will print a positive int 200 because bitwise AND with 0xFF will
 * zero all the 24 most significant bits that:
 * a) were added during upcasting to int which took place silently
 *    just before evaluating the bitwise AND operator.
 *    So the `b & 0xFF` is equivalent with `((int) b) & 0xFF`.
 * b) were set to 1s because of "sign extension" during the upcasting
 *
 * 1111 1111 1111 1111 1111 1111 1100 1000 (the int)
 * &
 * 0000 0000 0000 0000 0000 0000 1111 1111 (the 0xFF)
 * =======================================
 * 0000 0000 0000 0000 0000 0000 1100 1000 (200)
 */
System.out.println(b & 0xFF); // "200"

/*
 * You would typically do this *within* the method that expected an
 * unsigned byte and the advantage is you apply `0xFF` only once
 * and than you use the `unsignedByte` variable in all your bitwise
 * operations.
 *
 * You could use any integer type longer than `byte` for the `unsignedByte` variable,
 * i.e. `short`, `int`, `long` and even `char`, but during bitwise operations
 * it would get casted to `int` anyway.
 */
void printUnsignedByte(byte b) {
    int unsignedByte = b & 0xFF;
    System.out.println(unsignedByte); // "200"
}

답변

// 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

// Parse an unsigned byte
byte b = (byte) Integer.parseInt("200");

// Print an unsigned byte
System.out.println("Value of my unsigned byte: " + (b & 0xFF));

// 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

byte ratio = (byte) ((b1 & 0xFF) / (b2 & 0xFF));

int anUnsignedByte = (int) aSignedByte & 0xff;

int unsignedInt = Byte.toUnsignedInt(myByte);

byte b = 255;
System.out.println((b < 0 ? 256 + b : b));

public static char toUnsigned(byte b) {
    return (char) (b >= 0 ? b : 256 + b);
}