java - Some elements are just magically not removed from ArrayList -

ok here's block of code wrote :

public arraylist<location> possiblemoves() {    arraylist<location> a1 = new arraylist<location>(); // array contain       possible locations    board testb = new board(); // test board test if locations valid or not    // locations have x & y coordinates            a1.add(new location(getcurrentlocation().getx() - 1,                    getcurrentlocation().gety() + 1));           a1.add(new location(getcurrentlocation().getx() + 1, getcurrentlocation().gety() - 1));           a1.add(new location(getcurrentlocation().getx() - 1, getcurrentlocation().gety() - 1));           a1.add(new location(getcurrentlocation().getx() + 1, getcurrentlocation().gety() + 1));           (int = 0; < a1.size(); i++) {                 try {                     tower testtower = testb.getgrid()[a1.get(i).getx()][a1.get(i).gety()];                 }catch(arrayindexoutofboundsexception e) {                     a1.remove(a1.get(i));                 }           }          return a1;       } 

when remove element, position of following ones decreased. i. and, can use remove(int).

for (int = 0; < a1.size(); i++) {     try {         tower testtower = testb.getgrid()[a1.get(i).getx()][a1.get(i).gety()];     } catch(arrayindexoutofboundsexception e) {         a1.remove(i--);     } }