Multiple operations in map method using streams in Java8

Question

Given list of customers, I need to create another list with first names of customers in upper case. This is the code in java-

List<String> getFirstNames(List<Customer> customers)
{
    List<String> firstNames = new ArrayList<>();
    for(Customer customer: customers) {
        firstNames.add(StringUtils.uppercase(customer.getFirstName());
    }
    return firstNames;
}

How do I write this method using lambda in java8. I could use streams in this way, to convert to list-

customers.stream().map(Customer::getFirstName).collect(Collectors.toList());

But, how can I convert firstName to upper case, using this?

With method references customers.stream().map(Customer::getFirstName).map(StringUtils::uppercase).collect(toList()); — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Jun 12, 2015 at 2:14
Any reason to use StringUtils.uppercase(customer.getFirstName()) instead of simply customer.getFirstName().toUpperCase()? — Holger
– Holger, Commented Jun 12, 2015 at 13:46
@SotiriosDelimanolis Shouldn't we prefer to do it in one line as in the answer instead of doing it in 2 iterations? — Optimus Prime
– Optimus Prime, Commented Apr 5, 2018 at 16:03

dkatzel · Accepted Answer · 2015-06-12 00:24:33Z

4

Easiest way is to write your own lambda expression that does the conversion to uppercase for you:

 List<String> firstNames = customers.stream()
                         .map(customer->StringUtils.uppercase(customer.getFirstName()))
                        .collect(Collectors.toList());

answered Jun 12, 2015 at 0:24

dkatzel

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Comments

skyrays · Accepted Answer · 2020-09-11 13:52:47Z

1

Even in your code you are taking the customer name and then doing toUpperCase.

      List<String> firstNames = customers.stream()
                    .map(customer-> customer.getFirstName())
                    .map(firstName -> StringUtils.uppercase(firstName))
                    .collect(Collectors.toList())

answered Sep 11, 2020 at 13:52

skyrays

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