递归查找字符串中最大的ASCII字符- java

public class MaxAsciiCharFinder {
    public static char findMaxAsciiChar(String str) {
        if (str == null || str.length() == 0) {
            throw new IllegalArgumentException("Input string cannot be null or empty");
        }
        
        return findMaxAsciiCharHelper(str, 0, str.charAt(0));
    }
    
    private static char findMaxAsciiCharHelper(String str, int index, char maxChar) {
        if (index == str.length()) {
            return maxChar;
        }
        
        char currentChar = str.charAt(index);
        if (currentChar > maxChar) {
            maxChar = currentChar;
        }
        
        return findMaxAsciiCharHelper(str, index + 1, maxChar);
    }
}