Generic and dynamically associated type

Question

Probably, what I will ask is a terrible question, as the JAVA is strong-type language, but I will ask it, to be sure.

I wanted to implement few models, to which jackson will map to. Let's say that we have a: SomeObject which have a property value. SomeObject is an interface:

interface SomeObject <T> {
    T getValue();
}

Value can be a Boolean, can be a List, or can be a simple string. ObjectOne and ObjectTwo implements SomeObject I'm wondering, if we will have such object:

List<SomeObject> someObject = new ArrayList<>();

And we will have in that list: ObjectOne, ObjectTwo if there is a possibility to call getValue on each of those object, and without casting it to given class, get the proper value? I know I can do something like that:

(String) list.get(0).getValue();

but is there a way to get such results:

String firstItemIsAString = list.get(0).getValue();
ArrayList secondItemIsAnArrayList = list.get(1).getValue();

I know that this is not a javascript, but maybe with some help of Generics this may be achivable? I will add that item in the list of SomeObjects will be added in such way:

List<SomeObject> list = new ArrayList<>();
list.add(new ObjectOne<String>());
list.add(new ObjectTwo<ArrayList>());

No, generics are a compile time construct. The types must be known at compile time. — Sotirios Delimanolis, Apr 02 '15 at 22:21
Perhaps if we knew why you wanted to do this we could suggest a viable alternative. — Radiodef, Apr 02 '15 at 22:30
Do you know what the actual types will be of each particular element of the list? — Bohemian, Apr 02 '15 at 22:40

score 2 · Accepted Answer · answered Apr 02 '15 at 22:38

As soon as you put a Boolean and an ArrayList together into some Collection, the generic type of the Collection will have to be some common type of both, which just leaves Object - thus you have no information about the types in the collection at all.

To answer your question directly: no, there is no way of saving the type of something within generics as those are gone during runtime.

score -1 · Answer 2 · answered Apr 02 '15 at 22:32

-1

Perhaps a helper method would help you pretend Java was less type safe:

public interface SomeObject <T> {
    T getValue();
}
public static void main(String...args){
    List<SomeObject<?>> objectList=new ArrayList<SomeObject<?>>();
    String firstItemIsAString = converter(objectList.get(0).getValue());
}
public static <t> t converter(Object input){
    return (t) input;
}

answered Apr 02 '15 at 22:32

Andreas

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Perhaps you should explain what this actually does, what its limitations are and why it may or may not be useful. – Radiodef Apr 02 '15 at 23:55

Generic and dynamically associated type

2 Answers2