How to split an ArrayList into multiple smaller ArrayLists in Java?-javaTutorial-php.cn

How to split an ArrayList into multiple smaller ArrayLists in Java?

Barbara Streisand

Release： 2024-11-25 03:22:11

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How to split an ArrayList into multiple smaller ArrayLists in Java?

Splitting an ArrayList into Multiple Smaller ArrayLists in Java

In Java, splitting an ArrayList into multiple smaller ArrayLists of a specified size requires a solution that allows for efficient portioning and potentially creates non-view sublists.

Using subList()

One approach is to utilize the subList(int fromIndex, int toIndex) method to obtain a view of a portion of the original list. This method does not create a new list but rather provides a reference to a segment within the existing ArrayList.

Example:

List<Integer> numbers = new ArrayList<>(Arrays.asList(5,3,1,2,9,5,0,7));

List<Integer> head = numbers.subList(0, 4);
List<Integer> tail = numbers.subList(4, 8);

System.out.println(head); // prints "[5, 3, 1, 2]"
System.out.println(tail); // prints "[9, 5, 0, 7]"

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Creating Non-View Sublists

However, if you need the chopped lists to be independent and not a view of the original list, you can create a new ArrayList from the subList.

Example:

// chops a list into non-view sublists of length L
static <T> List<List<T>> chopped(List<T> list, final int L) {
    List<List<T>> parts = new ArrayList<>();
    final int N = list.size();
    for (int i = 0; i < N; i += L) {
        parts.add(new ArrayList<>(list.subList(i, Math.min(N, i + L))));
    }
    return parts;
}

List<Integer> numbers = Collections.unmodifiableList(Arrays.asList(5,3,1,2,9,5,0,7));
List<List<Integer>> parts = chopped(numbers, 3);

System.out.println(parts); // prints "[[5, 3, 1], [2, 9, 5], [0, 7]]"
parts.get(0).add(-1);
System.out.println(parts); // prints "[[5, 3, 1, -1], [2, 9, 5], [0, 7]]"
System.out.println(numbers); // prints "[5, 3, 1, 2, 9, 5, 0, 7]" (unmodified!)

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