CODEWITHSUNDEEP
javadesign-patterns
Lenik
Lenik

Reputation: 14458

A pattern about collection accessor transformation

How to call this pattern, and is there any existing apache-commons utility for this:

class Person {
    String getName();
}

List<Person> persons = ...;

// create a dynamic bean on the fly, which can be used as:
Object personXxxx = transformListOfBeans(Person.class, persons);
// so each of the bean properties now returns the list of the original property:
List<String> personNames = personXxxx.name;

// i.e. the transformation creates a new "type":
class PersonXxxx {
    List<String> getName();
}

How to call this kind of transformation? A proxy should keep the method signatures. So it is not a proxy, neither decorator.

Well, I can simply rename the generated property names to plural form, like:

personXxxx.names

This is no problem. I want to know if such pattern was already known so I don't have to choose the appropriate words myself.

Upvotes: 1

Views: 98

Answers (3)

Snehal
Snehal

Reputation: 7496

I don't think there is a pattern as such, but guava provides a simple way of transforming a collection of one to another. For the example:

List<Person> persons = ...;
Iterable<String> names = Iterables.transform(persons, new Function<Person, String>() {
    @Override
    public String apply(Person person) {
        return person.getName();
    }
});

Upvotes: 1

user949300
user949300

Reputation: 15729

A possibility is to declare an interface for all the methods, e.g. (leading I for clarity) INamable, IAgeable, ISexable etc. Cast the List<Person> to List<ISomething>. Obviously this has issues.

Upvotes: 0

Jean-Philippe Briend
Jean-Philippe Briend

Reputation: 3525

I don't think a tool exists for this. You have to code it :

List<String> names = new ArrayList<String>(persons.size());
for (Person person : persons) {
    names.add(person.getName());
}

Maybe you can use introspection to be more generic, but code is really simple.

Upvotes: 1

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