LeetCode - Reverse Bits

public class ReverseBits {
    
    public static int reverseBits(int n) {
        StringBuilder sb = new StringBuilder(Integer.toBinaryString(n));
        StringBuilder s = new StringBuilder(sb.reverse());
        if(s.length()!=32) {
            while(s.length() != 32) {
                s.append("0");
            }
        }
        //System.out.println(s);
        int ans = 0;
        for(int i=s.length()-1; i>=0; i--) {
            if(s.charAt(i) == ‘1‘) {
                //System.out.println(s.length()-1-i);
                ans += pow(2, s.length()-1-i);
            }
        }
        return ans;
    }
    public static int pow(int n, int m) {
        int ans = 1;
        for(int i=0; i<m; i++) {
            ans *= n;
        }
        ans = Math.abs(ans);
        return ans;
    }