Java: Error when translating English to Morse Code (Not a duplicate)

Question

I am creating a project that translate Morse Code into English and English into Morse Code. The program shall prompt the user to specify the desired type of translation, input a string of Morse Code characters or English characters, then display the translated results. All upper and lower case, numbers and punctuations could be ignored. And please do not use Hashtables and maps.

I manage to successfully finish writing the part to translate English to Morse. However, when translating Morse to English there seems to be a lot of errors going on. But I couldn't figure out why.

So anyone who's reading this, I would be so thankful if you help me solve the error! Any helps are appreciated. Thank you so much!

The error message that was displayed on the console was this :

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 3 at java.lang.String.substring(String.java:1950) at Project1.MoToEng(Project1.java:57) at Project1.main(Project1.java:30)

public class Translator
{
public static String[] morse = { ".- ", "-... ", "-.-. ", "-.. ", ". ",
        "..-. ", "--. ", ".... ", ".. ",

        ".--- ", "-.- ", ".-.. ", "-- ", "-. ", "--- ", ".--. ", "--.- ",
        ".-. ", "... ", "- ", "..- ",

        "...- ", ".-- ", "-..- ", "-.-- ", "--.. ", "|" };

public static String[] alphabet = { "a", "b", "c", "d", "e", "f", "g", "h",
        "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u",
        "v", "w", "x", "y", "z", " " };

public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    System.out.println("Input '1' to translate English to Morse Code.");
    System.out.println("Input '2' to translate Morse Code to English.");
    int kind = in.nextInt();

    if (kind == 1) {
        System.out.println("Please insert an alphabet string");
        String Eng = in.next();
        EngToMo(Eng);
    }
    if (kind == 2) {
        System.out.println("Please insert a morse string");
        String Mor = in.next();
        MoToEng(Mor);
    }

}

public static void EngToMo(String string1) { 
    String Upper1 = string1.toUpperCase();
    for (int i = 0; i < Upper1.length(); i++) {
        char character1 = Upper1.charAt(i);
        if (character1 != ' ') {
            System.out.print(morse[character1 - 'A'] + " ");
        } else {
            System.out.println(" | ");
        }
    }
}

public static void MoToEng(String string2) { 
int x = 0;
int y = 1;
String space = " ";
for (int i = 0; i < string2.length(); i++) {
    if(string2.substring(x,y).equals(space)){
        x++;
        y++;
    }
    else{
        y++;
        if(string2.substring(x,y).equals(morse[i])){
            System.out.println(alphabet[i]+ " ");
        }
    }
}
}
}

Answer 1

There are a few issues with this code.

The first is what is causing the exception,

Because y starts at 1 and increases by one each loop it will equal the length of string2 on its last iteration. This means, as strings are zero indexed, it will be one high than the last index in the string, hence the crash in string2.substring(x,y)

Secondly you are including spaces in your morse list and so the code is never able to match the last morse code in the string, so it would never match the string -. for example.

However it will match early if you just remove the spaces i.e. match -. in the string -.--.

You could simply use the split function to split the input string into an array split on " "

Sample code

public static void MoToEng(String string2) {
        int x = 0;
        char space = ' ';
        for (int y = 1; y <= string2.length(); y++) {
            String match = null;
            if (y == string2.length()) {
                // Reached the end of the string
                match = string2.substring(x);
            } else if (string2.charAt(y) == ' ') {
                // Reached the end of the word
                match = string2.substring(x,y);
                x = y+1;
                if (x == string2.length()) {
                    x--;
                }
            }

            if (match != null) {
                for (int j = 0;j < morse.length;j++) {
                    if (morse[j].equals(match+" ")) {
                        System.out.println(alphabet[j] + " ");
                    }
                }
            }
        }
    }

NOTE: You may run into problems as the scanner you are using to read from system.in will tokenize and only give you up to the first space. So if you use the Scanner class you only actually need

for (int j = 0;j < morse.length;j++) {
  if (morse[j].equals(string2+" ")) {
    System.out.println(alphabet[j] + " ");
  }
}

If you want to use the full match on input without relying on scanner to do the hard work change your second match to

if (kind == 2) {
  BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
  System.out.println("Please insert a morse string");
  try {
    MoToEng(br.readLine());
  } catch (IOException e) {
    e.printStackTrace();
  }
}

Obviously you can use an array list, split function and indexOf as suggested by user902383 but this answer is just to correct the crash in your code.

Answer 2

i simplified your method MoToEng, you need to change morse to be a list, and also i removed white spaces from entries

public static List<String> morse = Arrays.asList(".-", "-...", "-.-.",
            "-..", ".", "..-.", "--.", "....", "..", 
  "--..", "|");

and you need to change System.out.print(morse[character1 - 'A'] + " "); to System.out.print(morse.get(character1 - 'A') + " "); in EngToMo and it will work

and that should make it work

public static void MoToEng(String string2) {
        int x = 0;
        int y = 1;

        for (String token : string2.split("\\s+")) {

            int index = morse.indexOf(token);
            if (index > -1) {
                System.out.println(alphabet[index] + " ");
            }

        }
    }