Question

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How do you cast a List of objects from one type to another in Java?

Searched the internet a little, and found no nice way of doing it… My solution now is:

public class A {}
List<Object> obj = new ArrayList<Object>();
obj.add(new A());
// Ugly solution here:
List<A> a = (List<A>) (List) obj;

But this is quite ugly and gets a warning. No “official” way of doing this?

EDIT: To the guys who closed this: I was aware of the solution posted in How do you cast a List of objects from one type to another in Java? It is the same as the one I posted in my question (just adding the <?> after the first cast does exactly the same) I Was looking for something more “clean”. In the direction of using the Class<?> clazz = listobj.get(0).getClass way of getting the class and casting to the correct class at runtime (but no idea if something like that works… Eclipse doesn’t seem to like it anyway…)

Answer 1

List<Object> obj = new ArrayList<Object>();
obj.add(new A());

It is not the right way to write code. Basically you are creating a generic List and adding Object to it and it type unsafe and keep any Object type.

List<Object> obj = new ArrayList<Object>();
obj.add(new A());
obj.add(new String("str"));
obj.add(1);

It is recommended to create type-safe List like List<A> obj = new ArrayList<A>();

you can do this in such a way –

public <T>List<T> castCollection(List srcList, Class<T> clas){
    List<T> list =new ArrayList<T>();
    for (Object obj : srcList) {
    if(obj!=null && clas.isAssignableFrom(obj.getClass()))
        list.add(clas.cast(obj));
    }
    return list;
}