I am making a project for university, and I am currently stuck on something. I need help on how to make a bit of code repeat. I have two ufo's that go left to right (ufo) and right to left across the screen (ufo2) but I need them to do it over and over again. 

2. PImage space;
3. PImage trader;
4. PImage trader2;
5. PImage ship;
6. PImage ufo;
7. PImage ufo2;
8. PImage earth;
9. PImage uranaus;
10. PImage mars;
11. PImage venus;
12. float x;
13. float y;
14. int posx;
15. int posy;
16. 
    
17. boolean left, right, up, down;
18. boolean runOnce = true;
19. 
    
20. void setup() {
21.   size (1249, 768);
22.   smooth();
23.   space = loadImage("space.png");
24.   trader = loadImage("trader.png");
25.   trader2 = loadImage("trader2.png");
26.   ufo = loadImage("ufo.png");
27.   ufo2 = loadImage("ufo2.png");
28.   earth = loadImage("earth.png");
29.   uranaus = loadImage("uranaus.png");
30.   venus = loadImage("venus.png");
31.   x = 50;
32.   y = 1200;
33. }
34. 
    
35. 
    
36. void draw() {
37.   background(space);
38.   imageMode(CENTER);
39.   fill(256, 165, 0);
40.   image(trader2, 600 + posx, 700 + posy);
41.   image(ufo, x, 600);
42.   image(ufo2, y, 500);
43.   image(earth, 1030, 25);
44.   image(uranaus, 630, 25);
45.   image(venus, 230, 25);
46.   x +=4;
47.   y -=4;
48. }
49. 
    
50. void keyPressed()
51. {
52.   if (keyCode== RIGHT)
53.     posx+=10;
54.   if (keyCode== LEFT)
55.     posx-=10;
56.   if (posx<0) posx=0;
57.   if (posx>width) posx=width;
58.   if (keyCode== DOWN)
59.     posy+=10;
60.   if (keyCode== UP)
61.     posy-=10;
62.   if (posy<0) posy=0;
63.   if (posy>height) posy=height;
64. }

Here is my code. Any help would be greatly appreciated :)!