BYTE,BYTE[] 問題

一個處理BYTE和其他類型轉換的類：

public class Tools{
 //16進制
    private static String HexCode[] = {
        "0", "1", "2", "3", "4", "5", "6", "7", "8", "9",
        "a", "b", "c", "d", "e", "f"
    };

    private Tools(){
    }
 
 //將byte類型轉換爲16進制字符串
    public static String byteToHexString(byte b){
        int n = b;
        if(n < 0)
            n = 256 + n;
        int d1 = n / 16;
        int d2 = n % 16;
        return HexCode[d1]+HexCode[d2];
    }

 //將byte數組轉換爲16進制字符串
    public static String byteArrayToHexString(byte b[]){
        String result = "";
        for(int i = 0; i < b.length; i++)
            result = result+byteToHexString(b[i]);
        return result;
    }

 
 //將byte數組第offset個元素起的4個字節轉換爲int值
    public static int byte2int(byte b[], int offset)
    {
        return b[offset + 3] & 0xff | (b[offset + 2] & 0xff) << 8 | (b[offset + 1] & 0xff) << 16 | (b[offset] & 0xff) << 24;
    }
 //將byte數組轉換爲int值
    public static int byte2int(byte b[])
    {
        return b[3] & 0xff | (b[2] & 0xff) << 8 | (b[1] & 0xff) << 16 | (b[0] & 0xff) << 24;
    }

 //將byte數組轉爲long值
    public static long byte2long(byte b[])
    {
        return (long)b[7] & (long)255 | ((long)b[6] & (long)255) << 8 | ((long)b[5] & (long)255) << 16 | ((long)b[4] & (long)255) << 24 | ((long)b[3] & (long)255) << 32 | ((long)b[2] & (long)255) << 40 | ((long)b[1] & (long)255) << 48 | (long)b[0] << 56;
    }

 //將byte數組第offset個元素起的8個字節轉爲long值
    public static long byte2long(byte b[], int offset)
    {
        return (long)b[offset + 7] & (long)255 | ((long)b[offset + 6] & (long)255) << 8 | ((long)b[offset + 5] & (long)255) << 16 | ((long)b[offset + 4] & (long)255) << 24 | ((long)b[offset + 3] & (long)255) << 32 | ((long)b[offset + 2] & (long)255) << 40 | ((long)b[offset + 1] & (long)255) << 48 | (long)b[offset] << 56;
    }
 
 //將int類型轉爲byte數組
    public static byte[] int2byte(int n)
    {
        byte b[] = new byte[4];
        b[0] = (byte)(n >> 24);
        b[1] = (byte)(n >> 16);
        b[2] = (byte)(n >> 8);
        b[3] = (byte)n;
        return b;
    }

/**
 *n 爲待轉數據，buf[]爲轉換後的數據，offset爲buf[]中轉換的起始點
 * 轉換後數據從低到高位
 */
    public static void int2byte(int n, byte buf[], int offset)
    {
        buf[offset] = (byte)(n >> 24);
        buf[offset + 1] = (byte)(n >> 16);
        buf[offset + 2] = (byte)(n >> 8);
        buf[offset + 3] = (byte)n;
    }

    public static byte[] short2byte(int n)
    {
        byte b[] = new byte[2];
        b[0] = (byte)(n >> 8);
        b[1] = (byte)n;
        return b;
    }

    public static void short2byte(int n, byte buf[], int offset)
    {
        buf[offset] = (byte)(n >> 8);
        buf[offset + 1] = (byte)n;
    }

    public static byte[] long2byte(long n)
    {
        byte b[] = new byte[8];
        b[0] = (byte)(int)(n >> 56);
        b[1] = (byte)(int)(n >> 48);
        b[2] = (byte)(int)(n >> 40);
        b[3] = (byte)(int)(n >> 32);
        b[4] = (byte)(int)(n >> 24);
        b[5] = (byte)(int)(n >> 16);
        b[6] = (byte)(int)(n >> 8);
        b[7] = (byte)(int)n;
        return b;
    }

    public static void long2byte(long n, byte buf[], int offset)
    {
        buf[offset] = (byte)(int)(n >> 56);
        buf[offset + 1] = (byte)(int)(n >> 48);
        buf[offset + 2] = (byte)(int)(n >> 40);
        buf[offset + 3] = (byte)(int)(n >> 32);
        buf[offset + 4] = (byte)(int)(n >> 24);
        buf[offset + 5] = (byte)(int)(n >> 16);
        buf[offset + 6] = (byte)(int)(n >> 8);
        buf[offset + 7] = (byte)(int)n;
    }
   
}

*************************************************************************************

byte[] b = {00,00,00,00};
int i = ((b[0] << 24) + (b[1] << 16) + (b[2] << 8) + (b[3] << 0));
System.out.println(i); 

System.out.println(Integer.parseInt(new String(b,0,4))); 

結果：
都是由BYTE[]轉換爲INT，但
第一條打印語句得到結果:0
第二條出錯，因爲new String(b,0,4)爲"    "

原因如下：

（1）每四個byte可轉換成一個int，因爲int=4 byte

取出4個byte
int i = (int)b[0] | ((int)b[1] << 8) | ((int)b[2] << 16) | ((int)b[3] << 24);

上面用的是+
（2）0轉換爲字符串是/0，把二進制零轉不成字符串的，因爲/0是不可見的