Java: How to read only int data from text file to perform calculation?

Question

I use a button to save user input to a text file and now i want to retrieve it to do a calculation. The text file is gets updated and new values are added. Here is an e.g of how the text file looks:

1. monday : 1 tuesday: 2 wednessday: 3

...etc

When there is a new input it will be added, so the updated text file looks like this:

1. monday : 1 tuesday: 2 wednessday: 3
2. monday : 4 tuesday: 1 wednessday: 3
3. monday : 6 tuesday: 5 wednessday: 6
4. monday : 7 tuesday: 6 wednessday: 5

Basically i want to compare the new input with the previous input. How do I only retrieve all the integers from the latest and last input?

or should i rather use excel?

Here is my code:

try (
    InputStream fs = new FileInputStream("data.txt");
    // not sure how to use the Charset.forname
    InputStreamReader isr = new InputStreamReader(fs, Charset.forName("UTF-8"));
    BufferedReader br = new BufferedReader(isr)) {
    for (String line1 = br.readLine(); line1 != null; line = br.readLine()) {
        comp = line1 - line2; //line1 being current line(4) and line2 being the previous(3)
    }
}

Answer 1

Simply:

1. Read your file by keeping only the 2 last lines,
2. Then using a regular expression extract the integers.

The corresponding code:

try (
    InputStream fs = new FileInputStream("data.txt");
    InputStreamReader isr = new InputStreamReader(fs, StandardCharsets.UTF_8);
    BufferedReader br = new BufferedReader(isr)) {
    // Previous line
    String prev = null;
    // Last line
    String last = null;
    String line;
    while ((line = br.readLine()) != null) {
        prev = last;
        last = line;
    }
    // Pattern used to extract the integers
    Pattern pattern = Pattern.compile("\\d+");
    // Matcher for the previous line
    Matcher matcher1 = pattern.matcher(prev);
    // Matcher for the last line
    Matcher matcher2 = pattern.matcher(last);
    // Iterate as long as we have a match in both lines
    while (matcher1.find() && matcher2.find()) {
        // Value of previous line
        int val1 = Integer.valueOf(matcher1.group());
        // Value of last line
        int val2 = Integer.valueOf(matcher2.group());
        // Do something here
    }
}

NB: This assume that we have the exact same number of integers in both lines, otherwise you could compare unrelated values.

---

Another approach in case you use Java 8, you could use non integers as separator then rely on splitAsStream(CharSequence input) to extract all your integers as a List:

...
// Non integers as a separators
Pattern pattern = Pattern.compile("\\D+");
// List of extracted integers in previous line
List<Integer> previous = pattern.splitAsStream(prev)
    .filter(s -> !s.isEmpty())
    .map(Integer::valueOf)
    .collect(Collectors.toList());
// List of extracted integers in last line
List<Integer> current = pattern.splitAsStream(last)
    .filter(s -> !s.isEmpty())
    .map(Integer::valueOf)
    .collect(Collectors.toList());
// Do something here