Java: how can I split an ArrayList in multiple small ArrayLists?

Transforming sublists into independent lists

When you want independence for your sublists, the revolution is quick, create new instances of ArrayList:

List<ArrayList<Integer>> independentLists = choppedLists.stream()
    .map(ArrayList::new)  // The clone factory
    .collect(Collectors.toList());
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Residual elements - Oh, the horror!

Worry not, I have a solution for when your list's size does not perfectly divide by the sublist's chosen size. This handles the remainders efficiently:

int remainder = list.size() % size;
if(remainder != 0) {
    choppedLists.add(new ArrayList<>(list.subList(list.size() - remainder, list.size())));
}
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Remember, remainders, like forgotten birthday dates, can cause unexpected surprises.

Leveraging libraries

Partitioning like a boss with Guava

Guava is your friend when you love conciseness:

List<List<Integer>> guavaPartitions = Lists.partition(originalList, size);
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Splitting in elegance with Apache Commons Collections

Apache Commons Collections has a gorgeous way to split ArrayLists too:

List<List<Integer>> apachePartitions = ListUtils.partition(originalList, size);
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Cruising with Java 8 Stream API

With Java 8 Streams, there is no limit! It's like the Bugatti of ArrayList partitioning:

AtomicInteger index = new AtomicInteger();
Collection<List<Integer>> streamPartitions = originalList.stream()
    .collect(Collectors.groupingBy(it -> index.getAndIncrement() / size))
    .values();
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