Sonnenhut Sonnenhut - 4 months ago 9
Java Question

Get list of attributes of an object in an List

When there is an

List<Person>
, is there a possibility of getting List of all
person.getName()
out of that?
Is there an prepared call for that, or do I have to write an foreach loop like:

List<Person> personList = new ArrayList<Person>();
List<String> namesList = new ArrayList<String>();
for(Person person : personList){
namesList.add(personList.getName());
}

Answer

Java 8 and above:

List<String> namesList = personList.stream()
                                   .map(Person::getName)
                                   .collect(Collectors.toList());

If you need to make sure you get an ArrayList as a result, you have to change the last line to:

                                    ...
                                    .collect(Collectors.toCollection(ArrayList::new));

Java 7 and below:

The standard collection API prior to Java 8 has no support for such transformation. You'll have to write a loop (or wrap it in some "map" function of your own), unless you turn to some fancier collection API / extension.

(The lines in your Java snippet are exactly the lines I would use.)

In Apache Commons, you could use CollectionUtils.collect and a Transformer

In Guava, you could use the Lists.transform method.

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