How does Integer.parseInt(string) actually work?

Question

Was asked this question recently and did not know the answer. From a high level can someone explain how Java takes a character / String and convert it into an int.

M

Answer 1

public class StringToInt {

    public int ConvertStringToInt(String s) throws NumberFormatException
    {
        int num =0;
        for(int i =0; i=48)&&((int)s.charAt(i)<=59))
            {
                num = num*10+ ((int)s.charAt(i)-48);
            }
            else
            {
                throw new NumberFormatException();
            }

        }
        return num; 
    }

    public static void main(String[]args)
    {
        StringToInt obj = new StringToInt();
        int i = obj.ConvertStringToInt("1234123");
        System.out.println(i);
    }

}