BitSet 与 Byte Array 类型转化 转发

Converting Between a BitSet and a Byte Array

There are no default methods for converting a  BitSet to and from a byte array. This example implements two methods to do the conversion. These methods make it possible to easily work with both  BitSet and  BigInteger and take advantage of their capabilities when needed.

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// Returns a bitset containing the values in bytes.
// The byte-ordering of bytes must be big-endian which means the most significant bit is in element 0.
public static BitSet fromByteArray(byte[] bytes) {
    BitSet bits = new BitSet();
    for (int i=0; i<bytes.length*8; i++) {
        if ((bytes[bytes.length-i/8-1]&(1<<(i%8))) > 0) {
            bits.set(i);
        }
    }
    return bits;
}

// Returns a byte array of at least length 1.
// The most significant bit in the result is guaranteed not to be a 1
// (since BitSet does not support sign extension).
// The byte-ordering of the result is big-endian which means the most significant bit is in element 0.
// The bit at index 0 of the bit set is assumed to be the least significant bit.
public static byte[] toByteArray(BitSet bits) {
    byte[] bytes = new byte[bits.length()/8+1];
    for (int i=0; i<bits.length(); i++) {
        if (bits.get(i)) {
            bytes[bytes.length-i/8-1] |= 1<<(i%8);
        }
    }
    return bytes;
}

//Comments

     

      

       

        

         

          
          

           
10 Dec 2010 - 1:46pm by Anonymous (not verified)
 
           

            
Please be aware the above example will lose 1 bit for every byte read if the highest order bit is set. (byte)(1<<7) = -128 in Java and therefore will never be >0. To fix this example change >0 to !=0.
            
Also, it would be easy and preferable to serialize to longs as the Java implementation does.
           
          
         
         

          
          

           
16 Feb 2011 - 12:08pm by Anonymous (not verified)
 
           

            
Note that the Java 7 specification provides methods for converting between BitSets and bytes/longs.