Reading certain double from text file into a list

Question

I have this code to read numbers (type double) from a text file to a list.

ArrayList listTest = new ArrayList();
try {
    FileInputStream fis = new FileInputStream(path);
    InputStreamReader isr = new InputStreamReader(fis, "UTF-16");
    int c;
    while ((c = isr.read()) != -1) {
        listTest.add((char) c);
    }
    System.out.println();
    isr.close();
} catch (IOException e) {
    System.out.println("There is IOException!");
}

However, the output is look like:

instead of

    11.147
    42.81735

How can add the number to list line by line?

score 2 · Answer 1 · answered Feb 05 '18 at 15:28

As you say that they are doubles, this will convert them to doubles and add them to a list of doubles. This also has the benefit of not adding anything which can't be parsed to a double to your list which gives a bit of data validation.

    List<Double> listTest = new ArrayList<Double>();
    try (BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(path), "UTF-16"))) {
        String line;
        while ((line = br.readLine()) != null) {
            try {
                listTest.add(Double.parseDouble(line));
            } catch (NumberFormatException nfe) {
                // Not a double!
            }               
        }
        System.out.println();
    } catch (IOException e) {
        System.out.println("There is IOException!");
    }

This is the most helpful answer so far. Just a minor point to be aware of: https://stackoverflow.com/a/21348893/8473028 — DodgyCodeException, Feb 05 '18 at 15:42

score 1 · Accepted Answer · answered Feb 05 '18 at 15:19

You can wrap the InputStreamReader in a BufferedReader which has readLine() method:

List<String> listTest = new ArrayList<String>();
try (BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(path), "UTF-16"))) {
    String line;
    while ((line = br.readLine()) != null) {
        listTest.add(line);
    }
    System.out.println(listTest);
} catch (IOException e) {
    System.out.println("There is IOException!");
}

Also, notice the try-with-resources statement which automatically closes the stream (If you are using JDK1.6 or lower, call close() method in a finally block). In your sample code, the stream doesn't close if there was an exception.

score 0 · Answer 3 · answered Feb 05 '18 at 15:20

In your code, you read the input char by char, that's why you see such an output. You can read the input file using Scanner in a cleaner way without struggling with the stream readers etc.

ArrayList listTest = new ArrayList();
try {
   Scanner scanner = new Scanner(new File(path));
   while (scanner.hasNext()) {
      listTest.add(scanner.nextLine());
   }
   scanner.close(); 
} catch (IOException e) {
   System.out.println("There is IOException!");
}

Reading certain double from text file into a list

3 Answers3