Repeated Substring Pattern

class Solution {
    public boolean repeatedSubstringPattern(String s) {
        int length = s.length();
        for(int i = 1; i<=length/2; i++){
            if(length % i == 0){
                int freq = length / i;
                String sub = s.substring(0,i);
                StringBuilder sb = new StringBuilder();
                for(int j=0;j<freq;j++){
                    sb.append(sub);
                }

                if(sb.toString().equals(s)) return true;
            }
        }
        return false;
    }
}

Input
s =
"abab"
Output
true
Expected
true