tenta isso
public ArrayList<Location> getBorder(int radius){
ArrayList<Location> locs = new ArrayList<>();
int bX = 0;
int bZ = 0;
for(int x = bX - radius; x<= bX + radius; x++){
for(int z = bZ - radius; z <=bZ + radius; z++){
locs.add(new Location(world, x, getHighestBlock, z));
}
}
return locs;
}