无法将元素添加到ArrayList

Question

i'm still a beginner in java , i am trying to make a pacman game so i tried to make grid to let monesters follow the player , so i made a list called nieghbours contains all the nieghbouring squares to the current square of the monester but when i had a problem first when adding squares to the nieghbours Array list :

• i have a method called chase to update the x,y of the monester before rendering

• i have a method called findNieghbours called in the chase method to find the nieghbours of the current square of the monester .

but an error apear that the nieghbours ArrayList is empty ( has size of 0 ) .

public ArrayList<Square> findNieghbours(){
     ArrayList<Square> nieghbours=new ArrayList();
     int currentX=current.getX();
     int currentY=current.getY();

     if(currentX<29&&!grid.get(currentY/30).get(currentX/30+1).isWall()){
       nieghbours.add(grid.get(currentX/30+1).get(currentY/30));
     }
     if(currentX>0&&!grid.get(currentY/30).get(currentX/30-1).isWall()){
        nieghbours.add(grid.get(currentX/30-1).get(currentY/30));
     }
     if(currentY<29&&!grid.get(currentY/30+1).get(currentX/30).isWall()){
        nieghbours.add(grid.get(currentX/30).get(currentY/30+1));
     }
     if(currentY>0&&!grid.get(currentY/30-1).get(currentX/30).isWall()){
       nieghbours.add(grid.get(currentX/30).get(currentY/30-1));
     }

     return nieghbours;

public void Chase(Square chasedSquare){
    ArrayList<Square> nieghbours=findNieghbours();

    Square lowest=nieghbours.get(0);   

     for(Square square : nieghbours){
       if((square.getX()-chasedSquare.getX()) * (square.getX()-chasedSquare.getX()) + ( square.getY()-chasedSquare.getY()) * ( square.getY()-chasedSquare.getY()) < (lowest.getX()-chasedSquare.getX()) * (lowest.getX()-chasedSquare.getX()) + (lowest.getY()-chasedSquare.getY()) * lowest.getY()-chasedSquare.getY()){

           lowest=square;
       }

     }
     current=lowest;
 }

the error apears at this line in chase method :

Square lowest=nieghbours.get(0);

he said it is empty has size 0

but when i change the third condition to :

if(currentY/30<29&&!grid.get(currentX/30+1).get(currentY/30+1).isWall()){
        nieghbours.add(grid.get(currentX/30).get(currentY/30+1));
     }

it works but not as i want ( in each corner it jumps in two steps to become on the the right of the player )

Answer 1

I suppose the grid is size 30 by 30. Is this correct?

Then currentX/30 and currentY/30 would be always 0 . Is this what you intended?

Did you mean currentX%30 and currentY%30 instead?

If you want to go over to the left side, when hitting the right side, you should use (currentX+1)%30 .