Reverse bit 32 unsigned integer - fail to see the issue - 32 bit int primitive in Java language, need to do (long)1 >> power

reverseBit32UnsignedIntegerD.java

public class Solution {
	public long reverse(long a) {
	    long ret = 0; 
	    int index=0; 
	    long power = 31; 
	    while(a > 0 && index < 32)
	    {
	        int val = (int)(a &1); 
	        
	        if(val == 1)
	            ret += (long)(1 << power); 
	            
	        a = a >>1; // right shift
	        index++; 
	        power--; 
	    }
	    
	    return ret; 
	}
}