Loading an Array from a File

Question

I am working on an assignment with the following instructions,

Write a method that will load an array of floating point numbers from a file named floats.txt that you create, and then return that array. Assume the first value in the file holds the size of the array. Be sure to call your method.

I have created the following file with the title floats.txt

5
  4.3
  2.4
  4.2
  1.5
  7.3

I have never written a method that will return an array, nor have I ever created an array that reads from a file. Not asking anyone to write the program for me, by any means, but would appreciate some suggestions to get me started. I have written the method header as follows,

  public static double[] floatingFile() throws IOException {
  Scanner fin = new Scanner(new File"floats.txt");

Thanks.

Answer 1

For Java 7 I would use 1 row code:

List<String> lines = Files.readAllLines(Paths.get("floats.txt"), StandardCharsets.UTF_8);

Read all lines from a file. This method ensures that the file is closed when all bytes have been read or an I/O error, or other runtime exception, is thrown. Bytes from the file are decoded into characters using the specified charset.

See Doc here

Answer 2

You need to read the file into memory, you can do that line by line following what is here:

How to read a large text file line by line using Java?

Once you have a line of the file you can add it to your array.

Answer 3

Have a look at the javadoc for Scanner: http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html

There are methods such as Scanner.next() that will return the next value in the file.

Answer 4

You can open the file and read the elements one by one while storing them in each array element till it reaches null. Are you familiar with ArrayList?

Answer 5

I would pass the path of the file to your constructor (as follows), you still need to add one or two things... see here for example.

/**
 * Read in a file containing floating point numbers and
 * return them as an array.
 * 
 * @param filePath
 *          The path to the file to read.
 * @return Any double(s) read as an array.
 */
public static double[] floatingFile(String filePath) {
  Scanner fin = null;
  try {
    // Open the file at filePath.
    fin = new Scanner(new File(filePath));
    // first read the size
    int advSize = 0;
    if (fin.hasNextInt()) {
      // read in an int.
      advSize = // DO SOMETHING TO READ AN INT.
    }
    // construct a dynamic list to hold the Double(s).
    List<Double> al = new ArrayList<Double>(advSize);
    // while there are Double(s) to read.
    while (fin.hasNextDouble()) {
      // read in a double.
      double d = // DO SOMETHING TO READ A DOUBLE.
      al.add(d);
    }
    // Construct the return array.
    double[] ret = new double[al.size()];
    for (int i = 0; i < ret.length; i++) {
      ret[i] = al.get(i);
    }
    return ret;
  } catch (FileNotFoundException ignored) {
  } finally {
    if (fin != null) {
      // close our file reader.
      fin.close();
    }
  }
  // Return the empty array.
  return new double[] {};
}

Answer 6

 public float[] readLines(String <your filename>){ //in the try block
    FileReader fileReader = new FileReader(filename);
    BufferedReader bufferedReader = new BufferedReader(fileReader);
    List<float> arrFloat = new ArrayList<float>();
    String line = null;
    while ((line = bufferedReader.readLine()) != null) {
        lines.add(line);
    }
    bufferedReader.close();
    return arrFloat.toArray(new floatArray[arrFloat]);
}