ArrayList of generic objects in java. Unchecked call to 'Class(T)' as a member of raw type 'Class'

Question

I have the following piece of code:

public class Coordinate<T>{
T coordinate;
//rest of class
}

and then i later try to create an ArrayList which contains various Coordinates like so:

ArrayList<Coordinate> location = new ArrayList<Coordinate>();

and finally i add some coordinates to the location

location.add(new Coordinate(0));
location.add(new Coordinate("A"));
location.add(new Coordinate(0.1f));

these location.add() calls gives me the following warning:

Unchecked call to 'Coordinate(T)' as a member of raw type 'Coordinate'

I have searched for this warning and found some hits, but i was not able to figure out from those answers how i could make my application work, because i would like the ArrayList location to be able to hold different types of Coordinates, so i cant do something like

ArrayList<Coordinate<Integer>> location = new ArrayList<Coordinate<Integer>>(); .

Perhaps I'm just going about the problem in the wrong way?

Thanks in advance.

Answer 1

If you want to mix just numbers the following can be used ( <> is the diamond from Java 7 and onwards, for earlier versions there is no type inference).

List<Coordinate<? extends Number>> location = new ArrayList<>();
location.add(new Coordinate<>(1));
location.add(new Coordinate<>(1.0));

If you want to use all sorts of Objects the following can be used:

List<Coordinate<?>> location = new ArrayList<>();
location.add(new Coordinate<>(1));
location.add(new Coordinate<>("Hello"));

Since you created the Coordinate object without the generic parameter you got the warning.

new Coordinate(0) -> Unchecked call to 'Coordinate(T)' as a member of raw type 'Coordinate'

By changing the creation of Coordinate to new Coordinate<>(1) or whatever type is needed you avoid that problem.

Answer 2

In you array list you are putting Number as well as String .

ie you are adding objects in your array list, so its type should be Object

Because it is parent of all the classes in java.

List<Coordinate<Object>> location = new ArrayList<Coordinate<Object>>();