Converting Letters from String to Numbers

Question

Hello I am new to java and I am having a hard time on converting the letters from strings to numbers for example, the user will input "I am Okay" and the output will become 901-13015-11-1-25 since, I = 9 space = 0 A = 1 M = 13 space = 0 O = 15 K = 11 A = 1 Y = 25. I tried using switch, but I am having a hard time, because the program will print what I input in the string, well here is the test code I created, I hope someone can help me or give me tips and advices.

import java.util.*;
public class New2
{
public static void main(String[] args) {

    Scanner input = new Scanner(System.in);
    System.out.print("Input the First string: ");
    String fs = input.nextLine();
    
    fstoInt(fs);
    System.out.println(fs);

}

public static int fstoInt(String fs) {
    int num = 0;
    switch (fs) {
    case "A":
        num = 1;
        break;
    case "B":
        num = 2;
        break;
    case "C":
        num = 3;
        break;
    case "D":
        num = 4;
        break;
    case "E":
        num = 5;
        break;
    case "F":
        num = 6;
        break;
    case "G":
        num = 7;
        break;
    }
    return num;
}
}

Answer 1

output will become 901-13015-11-1-25 since, I = 9 space = 0 A = 1 M = 13 space = 0 O = 15 K = 11 A = 1 Y = 25

I don't think you read the assignment properly.

That would mean that: AA becomes 11 . And K ... also becomes 11 . Not sure this is what you wanted.

switch (fs) {
    case "A":

assuming it's all consecutive, with "A" becoming 1, and "Z" becoming 26: characters are just numbers (their unicode value), and those letters are in sequence. So, instead of a gigantic switch block, all you need is:

int num = fs.charAt(0) - 'A' + 1;

this will turn "A" into 1, and "Z" into 26.

As the comments already said, your problem is that fs isn't just "A" . It's "Hello" . You need to loop through the characters. As space gets special treatment (turning into 0), and presumably anything that isn't "A" - "Z" should crash:

for (char c : fs.toCharArray()) {
    int num = charToCode(c);
}

and then write charToCode:

public int charToCode(char c) throws IllegalArgumentException {
    if (c == ' ') return 0;
    if (c >= 'A' && c <= 'Z') return c - 'A' + 1;
    throw new IllegalArgumentException(
      "Only spaces and capital letters allowed");
}