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Converting a list of objects to a list of optional objects in Java


Converting a list of objects to a list of optional objects in Java

By : Veeshal
Date : November 24 2020, 01:01 AM
will be helpful for those in need You forgot to collect the elements of the Stream in a list. It should be:
code :
List<Optional<Object>> convertedList  = originalList.stream()
                                                    .map((o) -> Optional.of(o))
                                                    .collect(Collectors.toList()); 
                                               //or .collect(Collectors.toCollection(LinkedList::new)); if you want a specific List implementation


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Converting a List of Strings to a List of custom made objects in Java using Lambda Expression

Converting a List of Strings to a List of custom made objects in Java using Lambda Expression


By : Manucci
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , If you add a constructor to your Person class that takes a string, you can just use:
code :
List<Person> people = persons.stream()
    .map(Person::new)
    .collect(Collectors.toList());
List<Person> people = persons.stream()
    .map(s -> { Person p = new Person(); p.setName(s); return p; })
    .collect(Collectors.toList());
Java 8 Streams : Converting a list of objects to a set of objects

Java 8 Streams : Converting a list of objects to a set of objects


By : xdada
Date : March 29 2020, 07:55 AM
it should still fix some issue Your code will almost compile, you just missed the parentheses off p.getId etc.:
code :
Set<Product> productPriceList = productsList.stream()
    .map(p -> new Product(p.getId(), p.getName(), p.getPrice()))
    .collect(Collectors.toSet());
Java 8 - Optional class on List of Objects

Java 8 - Optional class on List of Objects


By : user2009749
Date : March 29 2020, 07:55 AM
wish helps you It is generally not recommended to use Optional with collections. You can perfectly represent no results with an empty collection.
What you really want is to change your Car to avoid returning null countries. So inside your Car where you have String getCountry() change it to:
code :
Optional<String> getCountry() {
  return Optional.ofNullable(country);
}
c.getCountry()
 .filter(country -> country.equalsIgnoreCase("Germany")
 .ifPresent(country -> System.out.println(c.getCarName()+" car is from Germany"));
getCarList()
       .stream()
       .filter(this::isGerman)
       .forEach(car -> System.out.println(car.getCarName()+" car is from Germany");
boolean isGerman(Car car) {
  return c.getCountry()
     .filter(country -> country.equalsIgnoreCase("Germany")
     .isPresent();
}
Converting a list of large objects to a list of subset objects

Converting a list of large objects to a list of subset objects


By : user3037922
Date : March 29 2020, 07:55 AM
may help you . You could create a MiniAlarm class with a constructor that takes in Alarm as a parameter then use LINQ and a projection as follows:
code :
var result = myAlarms.Select(x=> new MiniAlarm(x)).ToList();
Converting a list of objects in java to a map of String key to List<objects> using one of its field as the key

Converting a list of objects in java to a map of String key to List<objects> using one of its field as the key


By : Jaysin
Date : March 29 2020, 07:55 AM
hope this fix your issue I have a list of objects List cars , Yes its very well supported.
Do like this :
code :
Map<String, List<Car>> youCarMap = yourCarList.stream().collect(
                Collectors.groupingBy(Car::getMake,
                    Collectors.mapping(c->c, Collectors.toList())));
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