Write from file to ArrayList

Question

For the program to work, it is necessary to write data from the file to the arraylist, but how to make the written element not equal to null in the loop? That is, so that the loop stops its execution as soon as it reads all the lines from the file

public static void readFromFile(String path, String filename) throws IOException {
    ArrayList<String> ip = new ArrayList<>();
    try {
        File file = new File(path + "\\" + filename);
        FileReader fr = new FileReader(file);
        BufferedReader br = new BufferedReader(fr);
        ip.add(br.readLine());
        while ((ip.add(br.readLine()) != null)) {
            //writing to a variable
        }
    } catch (IOException e) {
        System.out.println(e.getMessage());
    }
}

You should use try-with-resources to ensure that the FileReader is closed after reading from it. — Andy Turner
– Andy Turner, Commented Apr 7, 2022 at 16:37

Andy Turner · Accepted Answer · 2022-04-07 16:34:40Z

1

ip.add(...) returns a boolean. This code won't compile, because a boolean is a primitive, and thus can never be null.

Move the add inside the loop:

String line;
while ((line = br.readLine()) != null) {
  ip.add(line);
}

answered Apr 7, 2022 at 16:34

Andy Turner

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Comments

eternal · Accepted Answer · 2022-04-07 16:53:54Z

0

Here is the better way to read all lines:

Files.readAllLines(Paths.get("path_to_file"), StandardCharsets.UTF_8)

edited Apr 7, 2022 at 16:53

answered Apr 7, 2022 at 16:30

eternal

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