Sum using recursion - recursion

Question

Apologies for the basic question, I'm new to java and have been stuck on this for days.
I need firstly to convert letters to numbers and then using recursion to get the sum of those numbers. I think I am close but I'm also aware it very messy
public static void main(String[] arg) {
String str= "11";
//////////////////////////
String s = "helloworld";
String t = "";
for (int i = 0; i < s.length(); ++i) {
char ch = s.charAt(i);
if (!t.isEmpty()) {
t += " ";
}
int n = (int)ch - (int)'a' + 1;
t += String.valueOf(n);
}
System.out.println(t);
//////////////////////////////
int sum=0;
int x=Integer.parseInt(t);
int y=recursion(x);
System.out.println("The Sum of the digits is: "+ y);
}
public static int recursion(int y) {
if(y/10>=1) {
int tempvar =y%10;
int remain=y/10;
return tempvar + recursion(remain);
}
else {
return y;
}
}}

Answer 1

Ok so first of all, this line: int x=Integer.parseInt(t); will crash the program in runtime because the string t has spaces in it. So you need to remove this:
if (!t.isEmpty()) {
t += " ";
}
Second, parsing the string t to int is a problem, because the number in string t can get like very, very large. Parsing this very..very large number to an int will also produce an exception during runtime. So a better way to do this is leaving it as a string, loop over it and just add the digits in it.
I have two solutions here:
I loop on t and add the digits.
I assume you have some constraint on the size of t so as it can be parsed to int (or long), and then use recursion as you want.
public class Main {
public static void main(String[] args) {
String s = "hew";
String t = "";
for (int i = 0; i < s.length(); ++i) {
char ch = s.charAt(i);
int n = (int)ch - (int)'a' + 1;
t += String.valueOf(n);
}
System.out.println("t: "+t);
System.out.println("sum using string: " + getSumUsingString(t));
System.out.println("sum using int: " + getSumUsingLong(Long.parseLong(t), 0));
}
// the string function
private static long getSumUsingString(String t) {
long sum = 0;
for (int i = 0; i < t.length(); i++) {
sum += t.charAt(i)-48;
}
return sum;
}
// recursive function
private static long getSumUsingLong(long num, long sum) {
if (num==0) return sum;
sum += num % 10;
return getSumUsingLong(num / 10, sum);
}
}
Note:
You can use for example, BigInteger class in Java to deal with very large numbers if you really need to parse this string t to a number.