I'm not quite sure what you mean. Do you want generics?

Your question is... too generic, not specific enough.
Seriously, I don't understand the question either.
FYI, Processing language is actually a dialect of Java, so its objects are Java objects. It has full interoperability with Java.
Note that to transform a class into an object, you must do: SomeClass obj = new SomeClass(); or similar...

As said, all classes in Java are Object already, so an array of Object instances would do the trick.
But then you wouldn't do much things with that: these generic Objects are not usable as is.
It is much better to find out what these objects have in common. In Processing, we generally make methods like update() and display() to such movable and displayable objects.
So you can define an interface:
interface Sprite
{
  void update();
  void display();
}
and require all the objects you put in the array to implement this interface:
class Car implements Sprite
{
  Car { init stuff; }
  // These two are now mandatory, you can add other functions
  void update() { implement stuff; move shape; }
  void display() { implement stuff; display shape; }
}
and then you can create an array of Sprite instances:
Sprite[] sprites = new Sprite[10];
sprites[0] = new Car();
sprites[1] = new Dog(); // Dog also implements Sprite
and use them:
for (Sprite sprite : sprites)
{
  // You are sure all objects from the array have these methods
  sprite.update();
  sprite.display();
}
That's classical (and simple) object oriented programming.

thanks a lot PhiLho and calsign,