为什么最后一个字符不出现？

Question

I want to encode a String like ...----....--.-.-. to .3-4.4-2.1-1.1-1.1 - showing, that there are three dots first (.3), then four hyphens (-4) next and so on.

I nearly made it, but there's a mistake anywhere...

static String pointsAndLines(String s){

    StringBuffer encodedString = new StringBuffer();

    int counter = 1;
    char currentChar = s.charAt(0);

    for(int i=1; i<s.length(); i++){
        if(s.charAt(i) != currentChar){
            encodedString.append(String.valueOf(currentChar) + counter);
            currentChar = s.charAt(i);
            counter = 1;
        } else counter++;
    }

    return encodedString.toString();

}

But the output is this:

.3-4.4-2.1-1.1-1

The last .1 is missing - but why?

Answer 1

The loop is terminated once you hit the end of the string, and the last group isn't appended to the buffer. You could just explicitly append it:

for(int i=1; i<s.length(); i++){
    if(s.charAt(i) != currentChar){
        encodedString.append(String.valueOf(currentChar) + counter);
        currentChar = s.charAt(i);
        counter = 1;
    } else counter++;
}
encodedString.append(String.valueOf(currentChar) + counter); // Here

Answer 2

In your code:

encodedString.append(String.valueOf(currentChar) + counter);

the last .1 is not appended to the StringBuffer because you are taking the value of currentchar which holds the previous value that is - on index 16 and not . on index 17 when the loop has reached its end that is value of i is equal to String s length minus 1.

To get the output .3-4.4-2.1-1.1-1.1 you can use two for loops as follows:

 public class StackOverFlowStringBuffer {

    public static void main(String[] args) {

        System.out.println(pointsAndLines("...----....--.-.-."));
    }

    static String pointsAndLines(String s) {

        StringBuffer encodedString = new StringBuffer();

        int counter = 1;
        char currentChar;

        for (int i = 0; i < s.length(); i++) {
            currentChar = s.charAt(i);
            if (i < s.length() - 1) {
                for (int j = i + 1; j < s.length(); j++) {
                    if (s.charAt(j) != currentChar) {
                        encodedString.append(String.valueOf(currentChar) + counter);
                        counter = 1;
                        i = j - 1;
                        break;
                    } else {
                        counter++;
                    }
                }
            } else {
                encodedString.append(String.valueOf(currentChar) + counter);
            }
        }

        return encodedString.toString();

    }
}