Java-将此方法转换为for和while循环

Question

This is a question from a past exam paper. I am not too sure how to convert the extract method to a while and for loop.

I have attempted this question: the extract1 and extract2 methods but i know they are incorrect. The original method may not be useful but the exam requires you to show how to write methods differently. I wanted to know how they could be done for future reference.

String extractedThis = "";

public String extract(String text){
    if(text.length()==0){
        return extractedThis;
    } else {
        return extractedThis = text.charAt(0) + extract(text.substring(1));
    }
}

public String extract1(String text) {

    while (text != null) {
        extractedThis = text.charAt(0) + text.substring(1);
    }
    return extractedThis;
}

public String extract2(String text) {

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

        extractedThis = text.substring(i);
    }

    return extractedThis;

}

Answer 1

public String extractWhileLoop(String text) {
    extractedThis = "";

    while(text.length() > 0) {
        extractedThis += text.charAt(0);
        text = text.substring(1);
    }
    return extractedThis;
}

public String extractForLoop(String text) {
    extractedThis = "";
    for (int i = 0; i < text.length(); i++) {

        extractedThis += text.charAt(i);
    }

    return extractedThis;
}

However, I don't see what exactly your trying to achieve with these methods as the return their input, and could be done much easier

Answer 2

This function juste return the received string followed by the last character of the string (ie: 'abcd' => 'abcdd') in I read it correctly. It plays with a global variable in recursive calls, it's fun, but something to avoid at any cost :)

public String extract(String text){
  String lastChar = '';
  extractedThis = text;
  while(text.length() > 0) {
    lastChar = text.charAt(0);
    text = text.substring(1);
  }

  return extractedThis = extractedThis + lastChar;
}