如何在不使用split，substring或index的情况下剪切特定字符的字符串？

Question

for a school assignment, I have to cut the string off at a certain character. It takes an email as input, ex: name@mail.ca, and it has to print everything before the @ sign. We are not allowed to use substring, index or split. I've attached what i've tried so far.

public static void main(String[] args) {
    getPrefix("name@email.ca");
}


public static String getPrefix(String email) {
    String prefix = "";
    for (int i = 0; i < email.length(); i++) {
        if (email.charAt(i) == '@') {
            break;

        }

        prefix += email.charAt(i);
    }
    return prefix;
}

if i set the input as name@email.ca it prints: ame@email.caame@email.caame@email.caame@email.ca

So right now it is only taking away the first character, when instead I need it to take away everything from the @ onwards.

Also,I have to return the value rather than just print it, so how would I do that outside the loop.

Answer 1

Use StringBuilder to append each char of string before @ , If you can't use StringBuilder you can use String but i won't recommended to use string for this

 public static String getPrefix(String email) {

       StringBuilder builder = new StringBuilder();    // or String str = "";

       for (int i = 0; i < email.length(); i++) {
            if (email.charAt(i) == '@') {
                break;

            }
            builder.append(email.charAt(i));      //or str+=email.charAt(i);
       }
      return builder.toString();                   //or return str;
   }