Getting integer data from txt file in Java

Question

I want to read a text file with String and a few integers associated with this string.

This is the class I have to write in my program:

public List<Integer> Data(String name) throws IOException { return null; } 

I need to read the .txt file and find the name in this file with its data. And save it to ArrayList .

My question is: how to save it in ArrayList<Integer> when I have String in List .
That's what I think:

 Scanner s = new Scanner(new File(filename)); ArrayList<Integer> data = new ArrayList<Integer>(); while (s.hasNextLine()) { data.add(s.nextInt()); } s.close(); 

Answer 1

I would define the file as a field (in addition to filename , and I suggest reading it from the user's home folder) file

 private File file = new File(System.getProperty("user.home"), filename); 

Then you can use the diamond operator <> when you define your List . You can use try-with-resources to close your Scanner . You want to read lines. And you can split your line . Then you check to see if your first column matches the name. If so, try again and other columns will parse them before int . Sort of

 public List<Integer> loadDataFor(String name) throws IOException { List<Integer> data = new ArrayList<>(); try (Scanner s = new Scanner(file)) { while (s.hasNextLine()) { String[] row = s.nextLine().split("\\s+"); if (row[0].equalsIgnoreCase(name)) { for (int i = 1; i < row.length; i++) { data.add(Integer.parseInt(row[i])); } } } } return data; } 

Perhaps it’s much more efficient to scan the file once and save the names and fields as Map<String, List<Integer>> as

 public static Map<String, List<Integer>> readFile(String filename) { Map<String, List<Integer>> map = new HashMap<>(); File file = new File(System.getProperty("user.home"), filename); try (Scanner s = new Scanner(file)) { while (s.hasNextLine()) { String[] row = s.nextLine().split("\\s+"); List<Integer> al = new ArrayList<>(); for (int i = 1; i < row.length; i++) { al.add(Integer.parseInt(row[i])); } map.put(row[0], al); } } catch (Exception e) { e.printStackTrace(); } return map; } 

Then save this as fileContents as

 private Map<String, List<Integer>> fileContents = readFile(filename); 

And then implement your loadDataFor(String) method with fileContents like

 public List<Integer> loadDataFor(String name) throws IOException { return fileContents.get(name); } 

If your usage pattern reads file for many names, then the second is likely to be much faster.

Answer 2

If you want to use java8, you can use something like this.

Input.txt (should be in classpath):

 text1;4711;4712 text2;42;43 

Code:

 public class Main { public static void main(String[] args) throws IOException, URISyntaxException { // find file in classpath Path path = Paths.get(ClassLoader.getSystemResource("input.txt").toURI()); // find the matching line findLineData(path, "text2") // print each value as line to the console output .forEach(System.out::println); } /** searches for a line in a textfile and returns the line data */ private static IntStream findLineData(Path path, String searchText) throws IOException { // securely open the file in a "try" block and read all lines as stream try (Stream<String> lines = Files.lines(path)) { return lines // split each line by a separator pattern (semicolon in this example) .map(line -> line.split(";")) // find the line, whiches first element matches the search criteria .filter(data -> searchText.equals(data[0])) // foreach match make a stream of all of the items .map(data -> Arrays.stream(data) // skip the first one (the string name) .skip(1) // parse all values from String to int .mapToInt(Integer::parseInt)) // return one match .findAny().get(); } } } 

Output:

 42 43