How to Efficiently Read a Text File into an ArrayList in Java?

How to Read a Text File into an Array List in Java

Reading data from a text file into an array list can be accomplished in Java through a series of steps:

1. Get file contents as a list of strings: Using Files#readAllLines() returns all lines of the text file as a List.
2. Split each line into parts: Split each line using String#split() based on whitespace ("s ").
3. Convert each part to an integer: Parse the split parts into integers with Integer#valueOf().
4. Add integers to an array list: Utilize List#add() to incorporate each integer into an array list.

Putting it all together, here's the code:

List<Integer> numbers = new ArrayList<>();
for (String line : Files.readAllLines(Paths.get("/path/to/file.txt"))) {
    for (String part : line.split("\s+")) {
        Integer i = Integer.valueOf(part);
        numbers.add(i);
    }
}

If using Java 8, Stream API offers a concise alternative:

List<Integer> numbers = Files.lines(Paths.get("/path/to/test.txt"))
    .map(line -> line.split("\s+"))
    .flatMap(Arrays::stream)
    .map(Integer::valueOf)
    .collect(Collectors.toList());

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