Get list of attributes of an object in an List

Question

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 1

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)); 

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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.