Write a function to find the longest common prefix string amongst an array of strings.

Longest common prefix

public String longestCommonPrefix(String[] strs) {
        
        int n = strs.length;
        if (n == 0) 
            return "";
        if (n == 1)
            return strs[0];
        
        String prefix = strs[0];

        for (int i = 1; i < n; i++) {
            
            int j = 0;
            for (; j < prefix.length(); j++) {
                if (j >= prefix.length() || j >= strs[i].length() || strs[i].charAt(j) != prefix.charAt(j)) {
                    break;
                }
            }
            
            prefix = prefix.substring(0, j);
        }
        
        return prefix;
        
    }

it is showing error " no member named CharAt"