Cannot copy ArrayList without reference

Question

I am trying to make a basic chess AI. I have the class "Schach" that stores ArrayLists of the white Figures and the black Figures. When it's the AI's turn to make a move i first add all the moves and in teh next step I want to remove the ones that put itself in check. But for some reason The AI just executes every single possible move it has. I am not even updating the lists in the main class, the problem relies on the lists always having a reference to the ones in the AI class.

ALSO I already tried the clone() method and it didn't work. Any suggestions??

public class Ai {

    public static final Ai ai = new Ai();

    private static int maxY = 8;
    private static int maxX = 7;
    private static int minY = 1;
    private static int minX = 0;

    private static ArrayList<Entity> whiteFigures;
    private static ArrayList<Entity> blackFigures;
    private static ArrayList<Move> moves;

    public void processMoves() {

        moves = new ArrayList<Move>();

        resetLists();

        for (Entity e : blackFigures) {
            moves.addAll(calcMoves(e.getFigure(), blackFigures, whiteFigures));
        }

        System.out.println(moves.size());

        //removeCheckMoves();

        System.out.println(moves.size());

        executeMove(moves.get((int) (Math.random() * moves.size())));

        resetLists();

        Schach.turn = true;

    }

    private void removeCheckMoves() {

        Figure king = null;

        for (Entity e : blackFigures) {
            if (e.getFigure().type == Figure.king) {
                king = e.getFigure();
                break;
            }
        }

        ArrayList<Move> legalMoves = new ArrayList<Move>();
        for (Move m : moves) {
            resetLists();
            executeMove(m);
            if(!isLegal(king)) {
                legalMoves.add(m);
            }
        }
        
        moves = legalMoves;

    }
    
    private boolean isLegal(Figure king) {
        
        boolean check = false;
        for (Entity w : whiteFigures) {
            for (Move move : Utils.calcMoves(w.getFigure(), whiteFigures, blackFigures)) {
                if (Utils.numToPos(move.to).x == king.x && Utils.numToPos(move.to).y == king.y) {
                    check = true;
                    break;
                }
            }
            if(check) break;
        }
        return check;
        
    }

    private void executeMove(Move m) {
        for (Entity e : blackFigures) {
            if (e.getFigure().x == Utils.numToPos(m.from).x && e.getFigure().y == Utils.numToPos(m.from).y) {
                e.getFigure().x = Utils.numToPos(m.to).x;
                e.getFigure().y = Utils.numToPos(m.to).y;
                e.gotoSquare(Utils.posToNum(e.getFigure()) - 8);
                for (Entity w : whiteFigures) {
                    if (w.getFigure().x == e.getFigure().x && w.getFigure().y == e.getFigure().y) {
                        whiteFigures.remove(w);
                        break;
                    }
                }
                break;
            }
        }
    }

    private void resetLists() {
        
        whiteFigures = new ArrayList<Entity>();
        whiteFigures.clear();
        whiteFigures.addAll(Schach.whiteFigures);
        blackFigures = new ArrayList<Entity>();
        blackFigures.clear();
        blackFigures.addAll(Schach.blackFigures);

    }

//calcMoves function (works fine no reference here for sure)

}

EDIT

with this setup the ai shouldnt execute a move at all just calculate them...

EDIT 2 The resetLists function is the main issue (I guess)

Your lists are declared as *class members*. Do you know the consequences? — Timothy Truckle, May 26 '21 at 16:53
@TimothyTruckle You mean that they are static? I know that and it's suppossed to be like that. But I don't see how that would prohibit the AI to do it's work. Basically I just want to copy the static list from Schach to the static list in AI without them being connected to one another. — luis, May 26 '21 at 17:23
*"I know that and it's suppossed to be like that."* **--** Your knowledge is wrong. Especially for variables the `static` key word should be used only if you have a good reason to do so. — Timothy Truckle, May 26 '21 at 18:01

score 1 · Accepted Answer · answered May 26 '21 at 17:49

Alright so I fixed it myself. Here is my solution if someone will ever need it in the future :D

public static ArrayList<Entity> cloneList (ArrayList<Entity> array){
        ArrayList<Entity> arr = new ArrayList<Entity>();
        for(Entity e : array) {
            arr.add(cloneEntity(e));
        }
        return arr;
    }
    
    public static Entity cloneEntity(Entity e) {
        Entity entity = new Entity(e.getPosition(), [etc...]);
        return entity;
    }

Cannot copy ArrayList without reference

1 Answers1