Lambda expressions and nested arrays

Question

I'm trying to come up with some nice lambda expressions to build "desiredResult" from "customers" ArrayList. I implemented it in an old ugly way "for" loop. I know there should be nice one-liners, but I can't think of any method - nested arrays come into my way.

Iterable<List<?>> params;
Customer customer1 = new Customer("John", "Nowhere");
Customer customer2 = new Customer("Alma", "Somewhere");
Customer customer3 = new Customer("Nemo", "Here");
Collection<Customer> customers = new ArrayList<>();
customers.add(customer1);
customers.add(customer2);
customers.add(customer3);

Collection<List<?>> desiredResult = new ArrayList<>();
for (Customer customer : customers) {
    List<Object> list = new ArrayList<>();
    list.add(customer.getName());
    list.add(customer.getAddress());
    list.add("VIP");
    desiredResult.add(list);
}
params = desiredResult;

Mureinik · Accepted Answer · 2017-08-03 16:03:00Z

4

I'd just use Arrays.asList for creating the inner lists, which makes the problem much simpler:

Collection<List<?>> desiredResult = 
    customers.stream()
             .map(c -> Arrays.asList(c.getName(), c.getAddress(), "VIP"))
             .collect(Collectors.toList());

If you absolutely must have an ArrayList, just wrap the Arrays.asList call with it.

edited Aug 3, 2017 at 16:03

answered Aug 3, 2017 at 15:59

Mureinik

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3 Comments

lapkritinis Over a year ago

End result must be Iterable<List<?>>. Anything else can be changed/improved. What would be option without ArrayList?

Mureinik Over a year ago

@PutinasPiliponis as I've shown - my code does not use an ArrayList.

lapkritinis Over a year ago

Understood :) Question closed. Thanks for answer!

assylias · Accepted Answer · 2017-08-03 16:00:38Z

3

Here is a suggestion:

Collection<List<?>> desiredResult = customers.stream()
         .map(MyClass::customerToList)
         .collect(toList());

I have extracted the list building into a separate method for better readability - the corresponding method would look like this:

private static List<Object> customerToList(Customer c) {
  List<Object> list = new ArrayList<>();
  list.add(c.getName());
  list.add(c.getAddress());
  list.add("VIP");      
  return list;
}

edited Aug 3, 2017 at 16:00

answered Aug 3, 2017 at 15:58

assylias

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