How to have Java method return generic list of any type?

Question

private Object actuallyT;

public <T> List<T> magicalListGetter(Class<T> klazz) {
    List<T> list = new ArrayList<>();
    list.add(klazz.cast(actuallyT));
    try {
        list.add(klazz.getConstructor().newInstance()); // If default constructor
    } ...
    return list;
}

One can give a generic type parameter to a method too. You have correctly deduced that one needs the correct class instance, to create things (klazz.getConstructor().newInstance()).

No need to even pass the class:

public <T> List<T> magicalListGetter() {
    return new ArrayList<T>();
}

You can use the old way:

public List magicalListGetter() {
    List list = doMagicalVooDooHere();

    return list;
}

or you can use Object and the parent class of everything:

public List<Object> magicalListGetter() {
    List<Object> list = doMagicalVooDooHere();

    return list;
}

Note Perhaps there is a better parent class for all the objects you will put in the list. For example, Number would allow you to put Double and Integer in there.

Another option is doing the following:

public class UserList extends List<User>{

}

public <T> T magicalListGetter(Class<T> clazz) {
    List<?> list = doMagicalVooDooHere();
    return (T)list;
}

List<User> users = magicalListGetter(UserList.class);

`

Let us have List<Object> objectList which we want to cast to List<T>

public <T> List<T> list(Class<T> c, List<Object> objectList){        
    List<T> list = new ArrayList<>();       
    for (Object o : objectList){
        T t = c.cast(o);
        list.add(t);
    }
    return list;
}

Something like this

publiс <T> List<T> magicalListGetter(Class<T> clazz) {
    List list = doMagicalVooDooHere();
    return list;
}