解码DataOutputStream字节数组-移位产生奇数结果

Question

I've been looking at the java-source in order to work out how java encodes and decodes its byte arrays when using a DataOutputStream in conjunction with DataInputStream. (I'm writing a framework in C# which will be able to decode the results of a Java DataOutputStream).

The code for the encoding of a long to a stream of bytes is:

public final void More ...writeLong(long v) throws IOException {
    writeBuffer[0] = (byte)(v >>> 56);
    writeBuffer[1] = (byte)(v >>> 48);
    writeBuffer[2] = (byte)(v >>> 40);
    writeBuffer[3] = (byte)(v >>> 32);
    writeBuffer[4] = (byte)(v >>> 24);
    writeBuffer[5] = (byte)(v >>> 16);
    writeBuffer[6] = (byte)(v >>>  8);
    writeBuffer[7] = (byte)(v >>>  0);
    out.write(writeBuffer, 0, 8);
    incCount(8);
}

I am aware that this is using a series of Zero-Fill Right Shift's in order to convert the long into a series of 8 bytes.

In order to convert these back inside DataInputStream:

public final long More ...readLong() throws IOException {
    readFully(readBuffer, 0, 8);
    return (((long)readBuffer[0] << 56) +
    ((long)(readBuffer[1] & 255) << 48) +
    ((long)(readBuffer[2] & 255) << 40) +
    ((long)(readBuffer[3] & 255) << 32) +
    ((long)(readBuffer[4] & 255) << 24) +
    ((readBuffer[5] & 255) << 16) +
    ((readBuffer[6] & 255) <<  8) +
    ((readBuffer[7] & 255) <<  0));
}

Implementing these two methods (Seen here in my ideone script: code ) Seems to double the long. (You can probably see here i have removed the 5 (long) casts from the read method as these were causing the bit shift to happen in the wrong place)

My question is, as i am struggling to get my head around these bit shift operations, what is happening here? Is the way i have implemented it in some way different to the java-source?

Answer 1

我传递的是整数，而不是整数（即字节的一半），因此将输出结果加倍，因为它是将两组字节加在一起！