Collection iteration with forEach() in multiple threads or with forEach() and lambdas

Question

Let say I have an array with a thousands independent objects inside. Now I want to pass over each of them and perform the same operation, for instance, change the value of a specific field.

At first glance, there are multiple approaches in Java 8 to such task, for instance:

1. forEach(); with lambda expression inside:
   itemsArr.forEach(item -> item.setValue("test"));
2. forEach(); with iterator.
3. Separate array to a number batches/blocks and deal each batch in a separate thread. For instance: define 2 threads, elements from #0 to 999 will be executed in a thread «A» and the rest in a thread «B».

The final result should be: 100% of array elements should have cared.
What is the optimal approach to such task?

Update: There is a similar question but talks about another aspect, I'm interesting not in different types of loops performance comparison (while, for, forEach) but in a performance comparison of threats vs. lambdas in a task of array traversal?

Answer 1

Use a parallel stream, which the JVM will process using multiple threads:

Arrays.stream(itemsArr).parallel().forEach(item -> item.setValue("test"));

Although you seem to have a Collection, not an array, so:

itemsArr.parallelStream().forEach(item -> item.setValue("test"));