java - FindBugs:INT_VACUOUS_BIT_OPERATION

Question

为了将 int 转换为 IP 字符串，我使用了 Going from 127.0.0.1 to 2130706433, and back again 中的方法

private static final byte BYTE_MASK = (byte)0xff;

protected byte[] unpack(int bytes) {
    return new byte[] {
        (byte)((bytes >>> 24) & BYTE_MASK),
        (byte)((bytes >>> 16) & BYTE_MASK),
        (byte)((bytes >>>  8) & BYTE_MASK),
        (byte)((bytes       ) & BYTE_MASK)
   };
}

但是 Eclipse 中的 FindBugs 会生成错误:INT_VACUOUS_BIT_OPERATION。

INT_VACUOUS_BIT_OPERATION: bit operations that don't do any meaningful work.

为什么会这样以及如何解决？

Answer 1

我怀疑这是因为如果您也转换为byte，则不需要& BYTE_MASK。我假设 BYTE_MASK 是 0xff... 在这种情况下它基本上毫无意义。仅施法将具有相同的效果。

来自 section 5.1.3 of the JLS :

A narrowing conversion of a signed integer to an integral type T simply discards all but the n lowest order bits, where n is the number of bits used to represent type T. In addition to a possible loss of information about the magnitude of the numeric value, this may cause the sign of the resulting value to differ from the sign of the input value.