How can I consume for each elements of an optional list?

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I have a List which can be null;

List<T> list; // may or may not null

I want to process for each element with a consumer.

So far, I do.

        .ifPresent(stream -> stream.forEach(e -> {}));


ofNullable(eventDataList).ifPresent(v -> v.forEach(e -> {}));

Is there any easy or concise way to do this?

To avoid ugly null checking, use orElse(Collections.emptyList())

        .forEach(e -> {});

With static imports, it's pretty concise:

ofNullable(eventDataList).orElse(emptyList()).forEach(e -> {});

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Technically, if (list != null) { -> {...}); } is both shorter and more efficient in terms of CPU/memory usage than your variants.

Architecturally, if you have control over initialization of the list and its usage, it's often better to use either Collections.emptyList() instead of null (if the logic of your program allows) or make the list Optional from the very beginning. That would save you from necessity to make checks or create Optionals every time you want to use the list.

Working With Java 8 Optionals, How to work with Java 8 Optional methods for maximum data safety. Adding Element to as List or Collection If the value is present the provided Consumer will be invoked with the value contained as a parameter. Java LinkedList class is doubly-linked list implementation of the List and Deque interfaces. It implements all optional list operations, and permits all elements (including null). It implements all optional list operations, and permits all elements (including null).

I'm not sure that you can make it more concise. However, if you are frequently using the construct of looping over a nullable list and consuming each element, you could make a small class which does just that:

public class ListConsumer {
    public static <H> Consumer<List<H>> of(Consumer<H> consumer) {
        return hs -> hs.forEach(consumer);

You can then consume each element in a list as follows (e.g. print all Strings in list):

List<String> list = Arrays.asList("A", "B", "C");

Consumer<String> consumer = System.out::println;

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Model-Driven Engineering and Software Development: 7th , means the element is kept in any configuration, and, thus, e.g., the compilation for a model element with an optional features needs to get a refined annotation. strategy does not consume significantly more runtime for iterating the list of the fact that for each element missing an annotation its list of children elements is​  The user can access elements by their integer index (position in the list), and search for elements in the list. Unlike sets, lists typically allow duplicate elements. More formally, lists typically allow pairs of elements e1 and e2 such that e1.equals(e2) , and they typically allow multiple null elements if they allow null elements at all.

26 Reasons Why Using Optional Correctly Is Not Optional, Sometimes, when an Optional value is not present, all you want to do is to ifPresent() is a good alternative for isPresent()-get() pair when you just need to consume the value. public Optional<List<String>> fetchCartItems(long id) { This method creates a Stream of one element or an empty Stream (if  Term Definition; element: Required in the For Each statement. Optional in the Next statement. Variable. Used to iterate through the elements of the collection. datatype: Optional if Option Infer is on (the default) or element is already declared; required if Option Infer is off and element isn't already declared.

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  • why not simply if (list != null) { list.foreach(e->{});} ? Functional programming style is cool but not necessary to be always cleaner and more readable.
  • @AdrianShum Because I've already known that. Thanks.
  • I like that CPU/MEM concern. +1
  • I know this answer was given in 2016 before Java 9 so now, it can be handled using the native of() which would create an immutable list. I don't think it's good practice to allow an immutable list to be modified by adding elements to it.