Question

I need help converting Morse Code to English. I have already written and tested the code for translating English to Morse. My main problem is having all the characters in the Morse code together before translating it to an English character if that makes sense.

Example: “.” translates to E and … translates to S, but I don’t want the translation to start until it reaches …

Few Rules
-Spaces are used to separate Morse Letters
-| is used as an delimiter to separate words
-Cant use an hashmap 🙁

Here is my code

import java.util.Arrays;
import javax.swing.JOptionPane;

public class test3
{
public static void main ( String [] args )
{

    String s1 = "Morse";

    // Decide whether Morse code or English
    String decide = JOptionPane.showInputDialog("Enter 'English' for Morse to English code translation and 'Morse' for English to Morse code translation. Pay attention to Caps.");

    // Enter String & decide whether to convert to Morse or English
    String phrase = JOptionPane.showInputDialog("Enter the words you wish to translate.");

    if ( decide.equals( s1 ))
        toMorse( phrase );

    else
        toEnglish( phrase );
}

// Translate to Morse
public static void toMorse( String preTranslation )
{

    String[] english = {"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","1","2","3","4","5","6","7","8","9","0"};

    String[] morse = {".-","-...","-.-.","-..",".","..-.","--.","....","..", ".---",
            "-.-",".-..","--","-.","---",".--.","--.-",".-.","...","-","..-", 
            "...-",".--","-..-","-.--","--..",".----","..---","...--","....-",".....","-....","--...","---..","----.","-----"};
    // Remove uppercase
    String preTrans = preTranslation.toLowerCase();

    // Deletes spaces
    String phraseWithDelimiter = preTrans.replace( " ", "|");

    String[] translation = new String[phraseWithDelimiter.length()];
    String[] delimiter = {"|"};

    // Translate 
    for ( int arrayVar = 0, transArrayVar = 0, subStringVarB = 0, subStringVarE = 1; transArrayVar < phraseWithDelimiter.length();)
    {
        if( phraseWithDelimiter.substring(subStringVarB, subStringVarE).equals( delimiter[0] ) )
        {
            translation[transArrayVar] = delimiter[0];
            transArrayVar++;
            subStringVarB++;
            subStringVarE++;
        }
        else if ( phraseWithDelimiter.substring(subStringVarB, subStringVarE).equals( english[arrayVar] ) )
            {
                translation[transArrayVar] = morse[arrayVar];
                transArrayVar++;
                subStringVarB++;
                subStringVarE++;
                arrayVar = 0;
            }
            else
            {
                arrayVar++;
                if ( arrayVar == 35 )
                {
                    arrayVar = 0;
                    subStringVarB++;
                    subStringVarE++;
                    transArrayVar++;
                }
            }
    }
String morseSeparator = new String( " " );
arrayToString ( translation, morseSeparator );

}


//Convert array to string and print translation
public static void arrayToString(String[] trans, String separator) 
{
    String result = "";
    if (trans.length > 0) 
    {
            result = trans[0];    // start with the first element
            for (int i = 1; i < trans.length; i++)
                result = result + separator + trans[i];
        }
    System.out.println( result );
}

    // unfinished
public static void toEnglish( String preTranslation)
{
    }

I was thinking about making a for statement and assigning every character of the Morse code to a new string until I reach a white space and then using that to test but I’m unsure about how to do that.

Any help is appreciated thanks!

Answer 1

Create a regular expression containing all the Morse code sequences in order from longest to shortest.

 Pattern.compile("----\\.|-----|---\\.\\.|...")

and then just match that repeatedly against a string to get the longest valid Morse code sequence.

---

Alternatively, you can use a parser compiler like JavaCC.

SKIP : { " " }
TOKEN : { < A : "-." > }
TOKEN : { < B : "-..." > }
TOKEN : { < C : "-.-." > }
...

String translate() :
{ StringBuilder sb; }
{
  { sb = new StringBuilder(); }

  (
    letter(sb)
  )*
  <EOF>

  { return sb.toString(); }
}

void letter(StringBuilder sb) :
{}
{
  ( <A>
    { sb.append('a'); }
  | <B>
    { sb.append('b'); }
  | <C>
    { sb.append('c'); }
  ...
  )
}