How to find the first character of a String without using any API method

Question

Recently I was being asked this question in an interview:

Find the first character of a String without using any method from String class

Gave the following approaches, assuming str as a String:

1. str.charAt(0)
2. str.toCharArray()[0]
3. str.substring(0,1)

Can anyone suggest me the way it can be achieved?

Answer 1

Using Matcher API (and not String): we create a pattern that captures every character but only find the first one and print it (the dotall mode is enabled to handle the case where the first character is a line separator).

public static void main(String[] args) {
    Matcher matcher = Pattern.compile("(.)", Pattern.DOTALL).matcher("foobar");
    if (matcher.find()) {
        System.out.println(matcher.group(1)); // prints "f"
    }
}