String.equals-method 在比较两个字符串时总是返回 false

Question

My task for university my was to code a Morse-Code-Decoder. I have String-Array with every letter of the "morse-alphabet" in it. In a for-loop I cut the sentence in morsecode into it's "morseletters" using the substring-method. I've made another for-loop and and an if-statement, to check which letter from the "morse-alphabet" matches the current "morseletter". I've used the String.equals-method, but it does'nt work. Even if the two Strings are the same. I also printed the length of every String in the loop, to check if the Strings contained some unwanted spaces. But even though the Strings looked the same and had the same length, the condtion of my if-statement would never be true. The problem appers to be the equals-method. What do I have to change, so that my code works?

public class Morse {
private static String[] morsecodes = { ".-", "-...", "-.-.", "-..", ".",
         "..-.", "--.", "....", "..", ".---", "-.-", ".-..", "--", "-.",
         "---", ".--.", "--.-", ".-.", "...", "-", "..-", "...-", ".--",
         "-..-", "-.--", "--.." }; 

public static void  main (String args[]) {
    System.out.println(decodeMorseCode(".... . .-.. .-.. --- .-- --- .-. .-.. -.."));       
}
public static String decodeMorseCode(String morseText) {
    String realText = "";
    String morseLetter = "";
    int counter = 0;

    for(int i = 0; i < morseText.length(); i++) {   
        if((morseText.charAt(i)==' ')) {
            morseLetter = morseText.substring(counter,i);
            counter = i+1;
        }
        if(morseText.charAt(i)==' '||i+1==morseText.length()) {
            for (int j = 0; j < 26; j++) {
                if((morsecodes[j].equals(morseLetter))) { //this is the if-statemen which causes the problem
                    char c = (char)(j+97);
                    realText += c;
                }

                if(j+1<=morseText.length()) {
                    if(morseText.charAt(j)==' '&& morseText.charAt(j+1)==' ') {
                        realText += " ";
                    }
                }

            morseLetter = "";
            }
        }           
    }
    return realText;
}

}

Answer 1

Remove the line morseLetter = ""; as shown below, and your code will work.

    if(morseText.charAt(i)==' '||i+1==morseText.length()) {
        for (int j = 0; j < 26; j++) {
            if(morsecodes[j].equals(morseLetter)) { //this is the if-statemen which causes the problem
                char c = (char)(j+97);
                realText += c;
            }

            if(j+1<=morseText.length()) {
                if(morseText.charAt(j)==' '&& morseText.charAt(j+1)==' ') {
                    realText += " ";
                }
            }
            //morseLetter = "";
        }
    }           

Answer 2

There's some answers already, but maybe you would want to consider this approach:

public static String decodeMorseCode(String morseText) {
    String realText = "";
    String morseLetter = "";
    int counter = 0;
    List<String> morseMessage;

    //Easier splitting of the String with morse code
    String[] morseLetters = morseText.split(" ");
    morseMessage = Arrays.asList(morseLetters);

    for (String morse : morseMessage) {
        for (String letter : morsecodes) {
            if (morse.equals(letter)) {
                System.out.println(letter);
                //Here comes mapping from Morse-to-English.
            }
        }
    }
    return realText;
}

What I've done here is introduce an List that would store your message letter-by-letter and that makes it easier to loop through. This is done by first splitting the String into an Array containing individual letters, and then converting it into a List. I then compare each letter from the Morse code message to your Morse code "dictionary", and if you run this you will see that it is able to recognize each individual letter.

What is left is to create a Map to translate Morse code representation into English-alphabet letters. Note : maybe it would be better to not have an array of Morse codes, but have it as a Map with English mappings?

For example:

private static Map<Character, String> morseToEnglish;

public static void  main (String[] args) {
    morseToEnglish = new HashMap<Character, String>();
    morseToEnglish.put('a', ".-");
    morseToEnglish.put('b', "-...");
    morseToEnglish.put('c',  "-.-");
    morseToEnglish.put('d',  "-..");
    ...

And then loop and map:

    for (String morse : morseMessage) {
        for (String letter : morseToEnglish.values()) {
            if (morse.equals(letter)) {
                for (Character character : morseToEnglish.keySet()) {
                    if (morseToEnglish.get(character).equals(letter)) {
                        System.out.print(character);
                    }
                }
            }
        }
    }

The message you morse-encoded was 'helloworld' .