SpotBugs - BIT_IOR_OF_SIGNED_BYTE

Description

Loads a byte value (e.g., a value loaded from a byte array or returned by a method with return type byte) and performs a bitwise OR with that value. Byte values are sign extended to 32 bits before any any bitwise operations are performed on the value. Thus, if b[0] contains the value 0xff, and x is initially 0, then the code ((x « 8) | b[0]) will sign extend 0xff to get 0xffffffff, and thus give the value 0xffffffff as the result.

byte與int做or時，由於byte被轉成int，若此byte大於等於0x80，它將變成0xffffff80。

Solution

將byte與0xff做and，以去除其負數部分。

Example

Before:

	public static short byteArrayToShort(byte[] b) {
		final short ret;
		ret = (short) (b[0] << 8 | b[1] );
		return ret;
	}

After:

	public static short byteArrayToShort(byte[] b) {
		final short ret;
		ret = (short) (b[0] << 8 | b[1] & 0xff);
		return ret;
	}

如果將0x00與0xff傳入修改之前的程式碼，預期值為255(0x00ff)，但結果會為-1(0xffff)。