Add to list elements Async in Java

Question

I'm rather new to JAVA and have a problem similar to the one mentioned below, where I want to add elements to an array via async processing. However, the returned array is with size 0 and not the correct size.

// Iterate over the products and transform them asynchronously
List<String> transformed = new ArrayList<>();
for (Product product : products) {
    product.transform(rh -> {
        transformed.add(rh.result());
    });
}
// Check the transformed list.
System.out.println(transformed.size()) // should be 10 but is 0

I could not find a simple tested solution for this. What would be an example implementation for this in JAVA?

Answer 1

You just have to extends Thread in Product, then implement the function run() with an @Override. That's make you able to do your loop like this :

// Iterate over the products and transform them asynchronously
List<String> transformed = new ArrayList<>();
for (Product product : products) {
    transformed.add(product.start());
}
// Check the transformed list.
System.out.println(transformed.size()) // should be 10 but is 0

The .start() start a new Thread who run the méthode run().

You can also give your ArrayList transformed as an attribut for Product then in product .add() in transformed.

Answer 2

Not sure if I get your question, but one possible way to do it would be using a parallel stream and either using mapping or foreach on top of your products list.

I made some assumptions, just to create an example, but here's how it looks

    private void yourMethod(List products){
    List<String> transformed = products.parallelStream().map(this::transformation).collect(Collectors.toList());

    // Check the transformed list.
    System.out.println(transformed.size());
}

private String transformation(Product product){
    // do some transformation
    return "some transformed";
}