java 保存unsigned 数据方法

java中没有unsiged的设置，必须用signed的数据存储，也就是要多用些存储空间。
use a short to hold an unsigned byte, use a long to hold an unsigned int.
use a char to hold an unsigned short.
('char' type, which is a 2 byte representation of unicode, instead of the
 C 'char' type, which is 1 byte ASCII. Java's 'char' also can be used as
 an unsigned short, i.e. it represents numbers from 0 up to 2^16.)
short anUnsignedByte = 0;
 char anUnsignedShort = 0;
 long anUnsignedInt = 0;

int firstByte = 0;
 int secondByte = 0;
        int thirdByte = 0;
        int fourthByte = 0;

 byte buf[] = getMeSomeData();
 // Check to make sure we have enough bytes
 if(buf.length < (1 + 2 + 4)) 
   doSomeErrorHandling();
 int index = 0;
 
        firstByte = (0x000000FF & ((int)buf[index]))
 index++;
 anUnsignedByte = (short)firstByte;

        firstByte = (0x000000FF & ((int)buf[index]))
        secondByte = (0x000000FF & ((int)buf[index+1]))
 index = index+2;
 anUnsignedShort  = (char) (firstByte << 8 | secondByte);

        firstByte = (0x000000FF & ((int)buf[index]))
        secondByte = (0x000000FF & ((int)buf[index+1]))
        thirdByte = (0x000000FF & ((int)buf[index+2]))
        fourthByte = (0x000000FF & ((int)buf[index+3]))
        index = index+4;
 anUnsignedInt  = ((long) (firstByte << 24
                 | secondByte << 16
                        | thirdByte << 8
                        | fourthByte))
                       & 0xFFFFFFFFL;
// write it back as unsigned int, unsigned short, unsigned byte. 
buf[0] = (anUnsignedInt & 0xFF000000L) >> 24;
 buf[1] = (anUnsignedInt & 0x00FF0000L) >> 16;
 buf[2] = (anUnsignedInt & 0x0000FF00L) >> 8;
 buf[3] = (anUnsignedInt & 0x000000FFL);

 buf[4] = (anUnsignedShort & 0xFF00) >> 8;
 buf[5] = (anUnsignedShort & 0x00FF);

 buf[6] = (anUnsignedByte & 0xFF);