Sorting a 2D string array in Java in descending order and writing it to a file

Question

So I have to read out a string from a file in Java. It's for a highscore system. Each line of the file contains something similiar like this: "24/Kilian". The number in front of the / is the score and the text after the / is the name.

Now, my problem is that I have to sort the scores descending and write them back into the file. The new scores should overwrite the old ones.

I tried it but I can't get it working properly. I already wrote some code which reads the score + name line by line out of the file.

public static void sortScores() {
        String [][]scores = null;
        int i = 1;
        try (BufferedReader br = new BufferedReader(new FileReader("score.txt"))) {
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line);
                scores[i][0] = line.substring(0, line.indexOf("/"));
                scores[i][1] = line.substring(line.indexOf("/"), line.length());
                i++;
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

So, this code basically writes the score and the name in a 2D array like this:

score[0][0] = "24";
score[0][1] = "Kilian";

score[1][0] = "33";
score[1][1] = "Name";

score[2][0] = "45";
score[2][1] = "AnotherName";

I hope someone can help me with my problem.

Answer 1

Use Arrays.sort(arr, comparator) with a custom comparator:

Arrays.sort(theArray, new Comparator<String[]>(){

    @Override
    public int compare(final String[] first, final String[] second){
        // here you should usually check that first and second
        // a) are not null and b) have at least two items
        // updated after comments: comparing Double, not Strings
        // makes more sense, thanks Bart Kiers
        return Double.valueOf(second[1]).compareTo(
            Double.valueOf(first[1])
        );
    }
});
System.out.println(Arrays.deepToString(theArray));

Answer 2

I'd recomend you to make a new class Score which holds your data (score + name) and add a new instance of Score into a ArrayList for each row you read from the file. After that you can implement a Comparator and sort your ArrayList . It's much easier because you don't know how big your string array will get and you need to know that when you're working with arrays.

public class Score {
    public Score(int score, String name) {
        this.score = score;
        this.name = name;
    }

    int score;
    String name;

    // getter
}


List<Score> scoreList = new ArrayList<>();
String line;
while ((line = br.readLine()) != null) {
    scoreList.add(new Score(Integer.parseInt(line.substring(0, line.indexOf("/"))), line.substring(line.indexOf("/"), line.length())));
}

Collections.sort(scoreList, new Comparator<Score>() {
    public int compare(Score s1, Score s2) {
        return s1.getScore() - s2.getScore();
    }
}

// write to file

Answer 3

You can use java.util.Arrays 's sort -Method:

Arrays.sort(scores, (a, b) -> -a[0].compareTo(b[0]));

But this lead to the case that "3" will be above "23". So probably you should create new class which holds the value and use an ArrayList

Answer 4

You can try it:

 HashMap<Integer, String > map = new HashMap<>();

    try (BufferedReader br = new BufferedReader(new FileReader("score.txt"))) {
        String line;
        while ((line = br.readLine()) != null) {
            System.out.println(line);
            String[] lines = line.split("/");
            map.put(Integer.valueOf(lines[0]),lines[1]);
        }
        SortedSet<Integer> keys = new TreeSet<Integer>(map.keySet());
        keys.forEach(k -> System.out.println(map.get(k).toString() + " value " + k ));