java ----> 基础之位运算

 package test.ant;

 import java.util.Arrays;
 import java.io.UnsupportedEncodingException;

 public class BytesGet{
     public static void main(String[] args){
         BytesGet bytesGet = new BytesGet();
         byte[] res = bytesGet.getBytesByEncode("key");// key
         System.out.println(Arrays.toString(res));  // [107,101,121]
     }

     public byte[] getBytesByEncode(String str) {

         byte[] byteArray = new byte[100]; 

         try{
          byteArray = str.getBytes("UTF-8");
         }catch(UnsupportedEncodingException e){
             e.printStackTrace();
         }

          return byteArray;

     }
 }

下面代码摘自 jedis-2.8.1.jar JedisClusterCRC16.java

   private static final int[] LOOKUP_TABLE = { 0, 4129, 8258, 12387, 16516, 20645, 24774, 28903, 33032, 37161, 41290, 45419, 49548, 53677, 57806, 61935, 4657, 528, 12915, 8786, 21173, 17044, 29431, 25302, 37689, 33560, 45947, 41818, 54205, 50076, 62463, 58334, 9314, 13379, 1056, 5121, 25830, 29895, 17572, 21637, 42346, 46411, 34088, 38153, 58862, 62927, 50604, 54669, 13907, 9842, 5649, 1584, 30423, 26358, 22165, 18100, 46939, 42874, 38681, 34616, 63455, 59390, 55197, 51132, 18628, 22757, 26758, 30887, 2112, 6241, 10242, 14371, 51660, 55789, 59790, 63919, 35144, 39273, 43274, 47403, 23285, 19156, 31415, 27286, 6769, 2640, 14899, 10770, 56317, 52188, 64447, 60318, 39801, 35672, 47931, 43802, 27814, 31879, 19684, 23749, 11298, 15363, 3168, 7233, 60846, 64911, 52716, 56781, 44330, 48395, 36200, 40265, 32407, 28342, 24277, 20212, 15891, 11826, 7761, 3696, 65439, 61374, 57309, 53244, 48923, 44858, 40793, 36728, 37256, 33193, 45514, 41451, 53516, 49453, 61774, 57711, 4224, 161, 12482, 8419, 20484, 16421, 28742, 24679, 33721, 37784, 41979, 46042, 49981, 54044, 58239, 62302, 689, 4752, 8947, 13010, 16949, 21012, 25207, 29270, 46570, 42443, 38312, 34185, 62830, 58703, 54572, 50445, 13538, 9411, 5280, 1153, 29798, 25671, 21540, 17413, 42971, 47098, 34713, 38840, 59231, 63358, 50973, 55100, 9939, 14066, 1681, 5808, 26199, 30326, 17941, 22068, 55628, 51565, 63758, 59695, 39368, 35305, 47498, 43435, 22596, 18533, 30726, 26663, 6336, 2273, 14466, 10403, 52093, 56156, 60223, 64286, 35833, 39896, 43963, 48026, 19061, 23124, 27191, 31254, 2801, 6864, 10931, 14994, 64814, 60687, 56684, 52557, 48554, 44427, 40424, 36297, 31782, 27655, 23652, 19525, 15522, 11395, 7392, 3265, 61215, 65342, 53085, 57212, 44955, 49082, 36825, 40952, 28183, 32310, 20053, 24180, 11923, 16050, 3793, 7920 };
    // LOOKUP_TABLE.length=256
 public static int getCRC16(byte[] bytes, int s, int e)  // s = 0; e = res.length=3
   {
     int crc = 0;
     for (int i = s; i < e; i++) {
       crc = crc << 8 ^ LOOKUP_TABLE[((crc >>> 8 ^ bytes[i] & 0xFF) & 0xFF)];
     }
     return crc & 0xFFFF;
   }

位运算优先级：

1 << （左移），>>（右移），>>>（无符号右移）

2 &（位与）

3 ^ （位异或）

4 | （位或）

下面摘自《Java编程思想》

The shift operators also manipulate bits. They can be used solely with primitive, integral types. The left-shift operator (<<) produces the operand to the left of the operator after it has been shifted to the left by the number of bits specified to the right of the operator (inserting zeroes at the lower-order bits). The signed right-shift operator (>>) produces the operand to the left of the operator after it has been shifted to the right by the number of bits specified to the right of the operator. The signed right shift >> uses sign extension: If the value is positive, zeroes are inserted at the higher-order bits; if the value is negative, ones are inserted at the higher-order bits. Java has also added the unsigned right shift >>>, which uses zero extension: Regardless of the sign, zeroes are inserted at the higher-order bits. This operator does not exist in C or C++.

移位运算符也操纵位。它们只能用于原始的整体类型。左移运算符（<<）在向运算符右侧指定的位数向左移位后，在运算符左侧产生操作数（在低位位插入零）。带符号的右移运算符（>>）在向运算符右侧指定的位数向右移动后，产生操作符左侧的操作数。带符号的右移>>使用符号扩展：如果值为正，则在高阶位插入零;如果值为负，则在高阶位插入1。 Java还添加了无符号右移>>>，它使用零扩展：无论符号如何，都在高阶位插入零。 C或C ++中不存在此运算符。

If you shift a char, byte, or short, it will be promoted to int before the shift takes place, and the result will be an int. Only the five low-order bits of the right-hand side will be used. This prevents you from shifting more than the number of bits in an int. If you’re operating on a long, you’ll get a long result. Only the six low-order bits of the right-hand side will be used, so you can’t shift more than the number of bits in a long.

如果你移动一个char，byte或short，它将在转换发生之前被提升为int，结果将是一个int。只使用右侧的五个低位。这可以防止转移超过int中的位数。如果你长时间操作，你会获得很长的结果。只使用右侧的六个低位，因此您不能移位多于long的位数。

Shifts can be combined with the equal sign (<<= or >>= or >>>=). The lvalue is replaced by the lvalue shifted by the rvalue. There is a problem, however, with the unsigned right shift combined with assignment. If you use it with byte or short, you don’t get the correct results. Instead, these are promoted to int and right shifted, but then truncated as they are assigned back into their variables, so you get -1 in those cases.

移位可以与等号（<< =或>> =或>>> =）组合。左值由左移的左值替换。但是，无符号右移与分配相结合存在问题。如果您使用byte或short，则无法获得正确的结果。相反，它们被提升为int并右移，但随后被分配回变量，因此在这些情况下得到-1。