How to update each item in a list in Java 8 using Stream API

Question

I have a list defined as follows:

List<Integer> list1 = new ArrayList<>();
list1.add(1); 
list1.add(2);

How can I increase each list item by one (i.e. end the List [2,3]) using the Java 8 Stream API without creating a new list?

Answer 1

When you create Streamfrom List, you are not allowed to change the source Listfrom Stream, as indicated in the “Non-Intervention” in the package documentation . Failure to comply with this restriction may result in damage to the structure ConcurrentModificationExceptionor, even worse, damaged structure without exception.

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IntStream.range(0, list1.size()).forEach(ix -> list1.set(ix, list1.get(ix)+1));

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list1.replaceAll(i -> i + 1);

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Answer 2

. , , , Java 8: Math#incrementExact. ArithmeticException, int. , :

list1.replaceAll(Math::incrementExact);

Answer 3

You can iterate over indices using IntStreamin combination with forEach:

IntStream.range(0,list1.size()).forEach(i->list1.set(i,list1.get(i)+1));

However, this is not very different from the normal cycle and is probably less readable.

Answer 4

reassign the result to list1:

list1 = list1.stream().map(i -> i+1).collect(Collectors.toList());