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Saturday, April 3, 2010

Morsecode Interpreter Implementation

Perhaps the most famous of all coding schemes is the Morse code, developed by Samuel Morse in 1832 for use with the telegraph system. The Morse code assigns a series of dotsand dashes to each letter of the alphabet, each digit, and a few special characters (e.g., period, comma,colon, semicolon). In sound-oriented systems, the dot represents a short sound and the dash represents a long sound. Other representations of dots and dashes are used with light-oriented systems and signal-flag systems. Separation between words is indicated by a space or, simply, the absence of a dot or dash. In a sound-oriented system, a space is indicated by a short time during which no sound is transmitted.

This is a question I came across in Java How to Program book by Deitel (Highly recommended book) . The Question asks us to create a program that can interpret a given morse code into plain text and vice versa, and the program requires user to enter the morse code with a space separating each characters and three spaces separating each words. so here is the sample code table given in the book. but this is not the complete one, you can view the full morse code here.


So the following code is the interpreter class I wrote. It doesn’t handle user inputs or validate them but will throw an error for invalid morse codes. For user inputs we have to create a GUI or use command line. (Using java.swing.JFileChooser to browse for a code file or input the code directly into a text area. you name it.)

import java.util.Map;
import java.util.HashMap;
 * @author hasi_wk
public class MorseCode {
    private static final String placeHolder="?";
    private Map<String , String> txtmorse = new HashMap<String , String >();
    private Map<String , String> morsetxt = new HashMap<String , String >();
    public MorseCode(){
        //init maps
        txtmorse.put("A", ".-");    morsetxt.put(".-", "A");
        txtmorse.put("B", "-...");  morsetxt.put("-...", "B");
        txtmorse.put("C", "-.-.");  morsetxt.put("-.-.", "C");
        txtmorse.put("D", "-..");   morsetxt.put("-..", "D");
        txtmorse.put("E", ".");     morsetxt.put(".", "E");
        txtmorse.put("F", "..-.");  morsetxt.put("..-.", "F");
        txtmorse.put("G", "--.");   morsetxt.put("--.", "G");
        txtmorse.put("H", "....");  morsetxt.put("....", "H");
        txtmorse.put("I", "..");    morsetxt.put("..", "I");
        txtmorse.put("J", ".---");  morsetxt.put(".---", "J");
        txtmorse.put("K", "-.-");   morsetxt.put("-.-", "K");
        txtmorse.put("L", ".-..");  morsetxt.put(".-..", "L");
        txtmorse.put("M", "--");    morsetxt.put("--", "M");
        txtmorse.put("N", "-.");    morsetxt.put("-.", "N");
        txtmorse.put("O", "---");   morsetxt.put("---", "O");
        txtmorse.put("P", ".--.");  morsetxt.put(".--.", "P");
        txtmorse.put("Q", "--.-");  morsetxt.put("--.-", "Q");
        txtmorse.put("R", ".-.");   morsetxt.put(".-.", "R");
        txtmorse.put("S", "...");   morsetxt.put("...", "S");
        txtmorse.put("T", "-");     morsetxt.put("-", "T");
        txtmorse.put("U", "..-");   morsetxt.put("..-", "U");
        txtmorse.put("V", "...-");  morsetxt.put("...-", "V");
        txtmorse.put("W", ".--");   morsetxt.put(".--", "W");
        txtmorse.put("X", "-..-");  morsetxt.put("-..-", "X");
        txtmorse.put("Y", "-.--");  morsetxt.put("-.--", "Y");
        txtmorse.put("Z", "--..");  morsetxt.put("--..", "Z");
        txtmorse.put("1", ".----"); morsetxt.put(".----", "1");
        txtmorse.put("2", "..---"); morsetxt.put("..---", "2");
        txtmorse.put("3", "...--"); morsetxt.put("...--", "3");
        txtmorse.put("4", "....-"); morsetxt.put("....-", "4");
        txtmorse.put("5", "....."); morsetxt.put(".....", "5");
        txtmorse.put("6", "-...."); morsetxt.put("-....", "6");
        txtmorse.put("7", "--..."); morsetxt.put("--...", "7");
        txtmorse.put("8", "---.."); morsetxt.put("---..", "8");
        txtmorse.put("9", "----."); morsetxt.put("----.", "9");
        txtmorse.put("0", "-----"); morsetxt.put("-----", "0");
        txtmorse.put(".",".-.-.-"); morsetxt.put("-.-.-.",".");
        txtmorse.put(",", "--..--"); morsetxt.put("--..--",",");
        txtmorse.put("?", "..--.."); morsetxt.put("..--..", "?");
        txtmorse.put("'", ".----."); morsetxt.put(".----.","'");
        txtmorse.put("!", "-.-.--"); morsetxt.put("-.-.--","!");
    /** ToMorse code method converts given string to morse
     * @param message
     * @return Morse code of the message
    public String toMorse(String message){
        String morseCode="";
        String C ="";
        String code = "";
        /* Convert to uppercase*/
        message = message.toUpperCase();
        /* Iterate through every character and convert to morse with 1 space between
         * characters and 3 spaces between words, unknown characters will have a placeholder instead
        for(int i=0 ; i<message.length();i++){
            C = message.charAt(i)+"";
            if(C.equals(" "))
                morseCode+= "   " ;
                code = txtmorse.get(C);
                if (code==null)
                    morseCode+=placeHolder+" ";
                    morseCode+=code+" ";
        }// end of for loop
        return morseCode;
    /** Toplain method converts given morsecode into plain
     * @param morse code
     * @return plain text message
    public String toPlain(String morse){
        String plain="";
        String C="";
        /* Split morse into words. there are three spaces between every word
         * and one space between two characters
        String[] words = morse.split("    ");
        /* for every word , extract chracters and parse them
         *  word = morsecode version of the word
         *  char_ = morsecode of the character
         *  chars array contains the current word which is being converted
        for(String word:words){
            String[] chars=word.split(" ");
            for(String char_:chars){
                C= morsetxt.get(char_);
                if(C==null) return "Invalid morse code found! process terminated. ["+char_+"]";
            }// end of the inner loop
            // end of a word
            plain+=" ";
        }// end of the outer loop
        return plain;

Class file and the Doc can be downloaded form here

Happy coding..:)

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