So as part of my game, I have this:

1. projectiles=(Projectile[]) updateEntity(projectiles);
   
2. ...
   
3. Entity[] updateEntity(Entity[] e) {
4.         boolean[] marked=new boolean[e.length];
5.         for (int i=0; i<e.length; i++) marked[i]=(e[i].update());
6.         Entity[] newEnt=new Entity[0];
7.         for (int i=0; i<e.length; i++) if (marked[i]) newEnt=(Entity[]) p.append(newEnt,e[i]);
8.         return(newEnt);   
9.     }     
   

The point of this is that I can pass in my arrays of enemies, projectiles, etc that are currently in the gamestate, and it will update them and remove the dead ones from the list (the individual update functions return booleans as to whether the entity is still alive).
This function works until I try to use it's result (line 1), which give me a ClassCastException. If this is always the case, how does the append function get around this?

Another possibility: would there be a way to pass in the name of the Class I want as an argument, and create the newEnt array based on that in line 6?