JAVA -我如何编写带有字母和数字的转换（小写->大写，单个数字->其值的两倍，两位数字->其数字总和）程序？

Question

I was tasked to write a function that takes in user input as a string. For all characters which are numeric, double its value and, if it is two digits, then replace it with the sum of its digits (eg, 6 → 12 → 3 whereas 3 → 6). For all characters which are in uppercase, replace it with lowercase. For all characters which are in lowercase, replace it with uppercase (eg, m → M and N → n). The program should keep asking the user to enter strings until they either enter 'q' or 'Q' to quit. I have this so far, which works for the conversion of the letters. I'm not sure how to implement the other part into it and where it would go.

public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    String str1;
    System.out.print("Enter string: ");
    str1 = scan.nextLine();
    StringBuffer newStr = new StringBuffer(str1);

    for (int i = 0; i < str1.length(); i++) {

        //Checks for lower case character
        if (Character.isLowerCase(str1.charAt(i))) {
            //Convert it into upper case using toUpperCase() function
            newStr.setCharAt(i, Character.toUpperCase(str1.charAt(i)));
        }
        //Checks for upper case character
        else if (Character.isUpperCase(str1.charAt(i))) {
            //Convert it into upper case using toLowerCase() function
            newStr.setCharAt(i, Character.toLowerCase(str1.charAt(i)));
        }
    }

    System.out.println("String after conversion : " + newStr);
}

}

Answer 1

here is my approach

    public static String conversion(String inputString){
        String out = "";
        for(char c:inputString.toCharArray()){
            if(Character.isDigit(c)){
                int num = Integer.parseInt(String.valueOf(c))*2;
                if(num>=10){
                    char[] parts = String.valueOf(num).toCharArray();
                    int sum = 0;
                    sum+=Integer.parseInt(String.valueOf(parts[0]));
                    sum+=Integer.parseInt(String.valueOf(parts[1]));
                    out+=sum;
                }else out+=num;
            }else{
                if(Character.isUpperCase(c)) out+=Character.toLowerCase(c);
                else out+=Character.toUpperCase(c);
            }
        }
        return out;
    }