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1. Overview

In this tutorial, we'll explore different ways of listing sequences of numbers within a range.

2. Listing Numbers in a Range

2.1. Traditional for Loop

We can use a traditional for loop to generate numbers in a specified range:

public List<Integer> getNumbersInRange(int start, int end) {
    List<Integer> result = new ArrayList<>();
    for (int i = start; i < end; i++) {
        result.add(i);
    }
    return result;
}

The code above will generate a list containing numbers from start (inclusive) to end (exclusive).

2.2. JDK 8 IntStream.range

IntStream, introduced in JDK 8, can be used to generate numbers in a given range, alleviating the need for a for loop:

public List<Integer> getNumbersUsingIntStreamRange(int start, int end) {
    return IntStream.range(start, end)
      .boxed()
      .collect(Collectors.toList());
}

2.3. IntStream.rangeClosed

In the previous section, the end is exclusive. To get numbers in a range where the end is inclusive, there's IntStream.rangeClosed:

public List<Integer> getNumbersUsingIntStreamRangeClosed(int start, int end) {
    return IntStream.rangeClosed(start, end)
      .boxed()
      .collect(Collectors.toList());
}

2.4. IntStream.iterate

The previous sections used a range to get a sequence of numbers. When we know how many numbers in a sequence is needed, we can utilize the IntStream.iterate:

public List<Integer> getNumbersUsingIntStreamIterate(int start, int limit) {
    return IntStream.iterate(start, i -> i + 1)
      .limit(limit)
      .boxed()
      .collect(Collectors.toList());
}

Here, the limit parameter limits the number of elements to iterate over.

3. Conclusion

In this article, we saw different ways of generating numbers within a range.

Code snippets, as always, can be found over on GitHub.

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I just announced the new Learn Spring course, focused on the fundamentals of Spring 5 and Spring Boot 2:

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