Java adjacency matrix from .txt file won't read correctly

Question

UPDATE: With the help of @KyreX the code now correctly reads the file and prints the array of names as vertexes HOWEVER it is now printing the entire array of names as vertexes instead of appending one at each time resulting in this:

Gromit: Gwendolyn: Le-Spiderman: Wallace: Batman: Superman: 0 1 0 1 0 0 
Gromit: Gwendolyn: Le-Spiderman: Wallace: Batman: Superman: 1 0 0 1 0 1
Gromit: Gwendolyn: Le-Spiderman: Wallace: Batman: Superman: 0 0 0 0 1 0
Gromit: Gwendolyn: Le-Spiderman: Wallace: Batman: Superman: 1 1 0 0 0 0
Gromit: Gwendolyn: Le-Spiderman: Wallace: Batman: Superman: 0 0 1 0 0 0
Gromit: Gwendolyn: Le-Spiderman: Wallace: Batman: Superman: 0 1 0 0 0 0

The code resulting in this print looks like this:

    public String toString() {
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < numVertices; i++) {
            try {
                int q = 0;
                while (q < getNames("index.txt").length) {
                    s.append(getNames("index.txt")[q] + ": ");
                    q++;
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            for (boolean j : adjMatrix[i]) {
                s.append((j ? 1 : 0) + " ");
            }
            s.append("\n");
        }
        return s.toString();
    }

I am trying to create an adjacency matrix in java from a .txt file, the program is supposed to read the following file:

6

0 Gromit

1 Gwendolyn

2 Le-Spiderman

3 Wallace

4 Batman

5 Superman

It is then supposed to use this information to assign the vertexes of the matrix using the number preceding the name. E.g. 0 Gromit is position 0 etc. The 6 above the pairs is the number of pairs in the file, this must remain. The problem I have is that when I run my code instead of printing the names as the vertexes it prints the word "temp: " followed by the edges assigned to that position. This is my code:

    public String toString() {
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < numVertices; i++) {

            String vertexName = "temp";

            s.append(indexFile(vertexName, i) + ": ");
            for (boolean j : adjMatrix[i]) {
                s.append((j ? 1 : 0) + " ");
            }
            s.append("\n");
        }
        return s.toString();
    }

    // reading index.txt
    public String indexFile(String vertexNames, int g) {
        try {
            File indexObj = new File("index.txt");
            Scanner indexReader = new Scanner(indexObj);

            String indexData = indexReader.nextLine();

            if (indexData.startsWith(Integer.toString(g - 1)) == true) {
                String[] posAndName = indexData.split(" ");
                vertexNames = posAndName[1];
                System.out.print("it is " + posAndName[1]);
            }

            g++;

        } catch (FileNotFoundException e) {

            System.out.println("File Not Found.");
            e.printStackTrace();

        }
        return vertexNames;
    }

Answer 1

You should read the entire file at once. If you want to keep the content for later, you can store it in a variable.

private String[] getNames(String fileName) throws IOException {
    String[] names = null;
    try(Scanner in = new Scanner(new File(fileName))) {
        int maxNames = Integer.parseInt(in.nextLine()); // Get the number of names to read
        names = new String[maxNames];
  
        int storedCount = 0;
        while(storedCount < maxNames && in.hasNextLine()) {
            String line = in.nextLine(); // Read a line
            if(!line.isEmpty()) { // If the line is not empty
                names[storedCount] = line.split(" ", 2)[1]; // Split the line in at most 2 tokens separated by a space and store the second
                storedCount++; // Increment the count of names already stored
            }
        }
    }
    return names;
}

With this method you can get the first N-titles of the file with N being the value of the first line. You will have to handle the possible exceptions.

QUESTION UPDATED

As I said in the comment of the question, you should store the array and then use as many times as you want. If you call the method getNames() N times, you are reading the same entire file N times (really inefficient)

To get each name followed by its number, you need to iterate both elements (names and numbers) at the same time

String[] names = getNames("input.txt"); // read file once
for(int i = 0; i < names.length; ++i) {
    strBuilder.append(names[i]).append(": ").append(adjMatrix[i]).append("\n"); // use it many
}