Is it because the " this"  is not pointing at the main class ?

1. public void setup() {
2.   myDrone = new drone(this);
3.   size(400,400,P2D);
4.   frameRate(20); 
5. }
6. 
   
7. class drone
8. {
9.   PApplet pa;
   
10.   Gif drone_up;
11.   Gif drone_front;
12.   Gif drone_left;
13.   Gif drone_right;
14. 
    
15.   drone(PApplet mainClass)
16.   {
17.     pa = mainClass;
    
18.     drone_up = new Gif(pa, "drone_up.gif");
19.     drone_front = new Gif(pa, "drone_front.gif");
20.     drone_left = new Gif(pa, "drone_left.gif");
21.     drone_right = new Gif(pa, "drone_right.gif");
22.   }    
23. // [...]
24. }