java - Collision detection bug -

i've tried expand little on enemy spawning system using factory design pattern.

so have: enemy (abstract): enemytyp ea, b, c, d... etc., each of extend enemy.

i have this: (works)

public void spawnenemy(int type, int amount) {      enemy theenemy =  null;     (int i=1; i<amount+1; i++ ) {         theenemy = enemyfactory.makeenemy(type, 0-i*40, 400);         aliens.add(theenemy);         health.add(2);         system.out.println("attack message recieved "+i);     }     repaint(); } 

but cannot seem collision detection work.

public void checkcollisions() {              rectangle r3 = player.getbounds();            arraylist ms = player.getmissiles();            (int = 0; < ms.size(); i++) {                 missile m = (missile) ms.get(i);                 rectangle r1 = m.getbounds();                  (int j = 0; j<aliens.size(); j++) {                     enemy = (enemy) aliens.get(j);                     rectangle r2 = a.getbounds();                      if (r1.intersects(r2)) {                         m.setvisible(false);                         a.sethealth(-1);                         if(a.gethealth()==0){                         a.setvisible(false);                         }                  }}               }         } 

i believe it's because turning enemy (abstract) , why getting no collision.. when take item out of arraylist how can take out exact enemytype put in in spawnenemy() method? use theenemy variable , combination of instanceof? extremely confused.