Reverse Bits

Reverse bits of a given 32 bits unsigned integer.
For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192 (represented in binary as 00111001011110000010100101000000).
Follow up:
If this function is called many times, how would you optimize it?

Naive Way:Need to use another integer to store the reversed bits. Traversal target from low to high,  construct result from high to low.
The key here is to use ">>>" instead of ">>"
1000 >> 1 becomes 1100
1000 >>>1 becomes 0100

 public class Solution {  
   // you need treat n as an unsigned value  
   public int reverseBits(int n) {  
     int m = 0;  
     for(int i = 0;i < 32;i++)  
       if((n & (0x00000001 << i)) != 0) m |= (0x80000000 >>> i);  
     return m;  
   }  
 }