Java8 - How to store value from forEach in global variable ( lambda forEach )

Question

Am trying to iterate an ArrayList using Java 8 - Lambda forEach and to store the value in the global variable.

Am getting the error like type mis-match and am not able to typecast also.

Please see my code below.

Long product_id = listProducts.forEach(listproducts ->listproducts.getId());

My Previous approach : (without JAVA8 feature, now i want to change my code by using Java8)

 for(Product prod : listProducts)
        {
            product_id=prod.getId();
        }

forEach doesn't return anything. What exactly do you expect the output to be. You are processing a list of elements and seem to require a single value as the output. — Eran
– Eran, Commented Jan 9, 2018 at 10:08
Yes., it want to get a single value out of the list. previously i was using old method. But, just want to convert my code with new Java8 feactures. I will update my old code too. — Karthikeyan
– Karthikeyan, Commented Jan 9, 2018 at 10:13
Why do you use a loop in your original code? All but the final value assigned to product_id will be overwritten. — Eran
– Eran, Commented Jan 9, 2018 at 10:15
you may use like Long product_id = listProducts.get(listProducts.size()-1).getId(); no need any loop for this purpose. — Md. Kamruzzaman
– Md. Kamruzzaman, Commented Jan 9, 2018 at 10:29
You should fix the logic errors of your code first, then you may think about expressing the actual intent using a different API. — Holger
– Holger, Commented Jan 9, 2018 at 12:10

Md. Kamruzzaman · Accepted Answer · 2018-01-09 10:34:57Z

1

final Long prod[] = new Long[1];
listProducts.forEach(product->{         
    prod[0] = product.getId();      
});

Long product_id = prod[0];

answered Jan 9, 2018 at 10:34

Md. Kamruzzaman

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Georg Leber · Accepted Answer · 2018-01-09 13:13:25Z

1

sYou can not extract one single value from a list of values without aggregating it (max, min, sum, ...). In your old code you always saved the last id of your list of products. Is this intended? If so a loop does not make any sense. You can just retrieve the last element:

Long product_id = listProducts.get(listProducts.size() - 1);

But if you want to map the products to a list of their ids you can do something like:

List<Long> productIds = listProducts.stream().map(prod -> prod.getId()).collect(Collectors.toList());

UPDATE:
Or to get a single ID (if list is empty, the productId is null):

Long productId = listProducts.stream().map(prod -> prod.getId()).reduce((id1, id2) -> id2).orElse(null);

edited Jan 9, 2018 at 13:13

answered Jan 9, 2018 at 10:18

Georg Leber

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