Get list of attributes of an object in an List
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.
You might have done this but for others
using Java 1.8
List<String> namesList = personList.stream().map(p -> p.getName()).collect(Collectors.toList());
Try this
Collection<String> names = CollectionUtils.collect(personList, TransformerUtils.invokerTransformer("getName"));
Use apache commons collection api.
I think you will always need to do that. But if you will always need such things, then I would suggest to make another class, for example call it People
where personList
is a variable.
Something like this:
class People{
List<Person> personList;
//Getters and Setters
//Special getters
public List<string> getPeopleNames(){
//implement your method here
}
public List<Long> getPeopleAges(){
//get all people ages here
}
}
In this case you will need to call one getter only each time.
Not tested but this is the idea:
public static <T, Q> List<T> getAttributeList(List list, Class<? extends Q> clazz, String attribute)
{
List<T> attrList= new ArrayList<T>();
attribute = attribute.charAt(0).toUpperCase() + attribute.substring(1);
String methodName = "get"+attribute;
for(Object obj: personList){
T aux = (T)clazz.getDeclaredMethod(methodName, new Class[0]).invoke(obj, new Object[0]);
attrList.add(aux);
}
}