java - how to convert from str.substring(0, i) into str.charAt()? (to make equal)

Question

I tried in many times but don't know how to change str.substring(0,i) into str.charAt(i) Please help I tried to make a result as below but I struggle from str.substinrg(0,i) to str.charAt(i) If i would like to make a result as below, at this point, how should i have to change it?

repeatFront("Chocolate", 4) → "ChocChoChC"
repeatFront("Chocolate", 3) → "ChoChC"
repeatFront("Ice Cream", 2) → "IcI"

below code is not successfully correct

public String repeatFront(String str, int n) {

    int i;
    String newStr;

    for(i = 0; i < str.length(); i++)
    {
        newStr = Character.toString(str.charAt(n));
    }
    return str;
}

Answer 1

I have no clue if thats what you wanted, but the outputs are correct:

public static String repeatFront(String str, int n) {
    String newStr = "";

    for(int i = n; i > 0; i--) {
        for(int i2 = 0; i2 < i; i2++) {
            newStr = newStr + str.charAt(i2);
        } 
    } 

    return newStr;
}