Can a lambda be used to change a List's values in-place ( without creating a new list)?

Question

I am trying to determine the correct way of changing all the values in a List using the new lambdas feature in the upcoming release of Java 8 w

Answer 1

    List<String> list = Arrays.asList("Bob", "Steve", "Jim", "Arbby");
    list.replaceAll(String::toUpperCase);

Answer 2

With a popular library Guava you can create a computing view on the list which doesn't allocate memory for a new array, i.e.:

upperCaseStrings = Lists.transform(strings, String::toUpperCase)

A better solution is proposed by @StuartMarks, however, I am leaving this answer as it allows to also change a generic type of the collection.

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Another option is to declare a static method like mutate which takes list and lambda as a parameter, and import it as a static method i.e.:

mutate(strings, String::toUpperCase);

A possible implementation for mutate:

@SuppressWarnings({"unchecked"})
public static  List mutate(List list, Function function) {
    List objList = list;

    for (int i = 0; i 

Answer 3

You seem to have overlooked forEach, which can be used to mutate the elements of a List. Of course, that doesn't cover your use case entirely—it won't help if your elements are immutable or if you want to replace them completely. [edit: the next sentence relates to streams, not to collections as specified in the question] There is a good reason why you can't do those operations: they aren't parallel-friendly (this actually applies to forEach also) and the Stream API strongly discourages the use of sequential-only operations.