Moving objects around in a multi-dimensional array

Question

I'm working on making a board game for chess and checkers (and a few variations that I want to make). I've got a Board class that extends JPanel and sets up a doubly dimensioned array of JPanels to act as my board. Here's some of the code for my board class:

public class Board extends JPanel {

  private static final int COLS = 8;
  private static final int ROWS = 8;

  private JPanel[][] board = new JPanel[COLS][ROWS];
  private JPanel chessBoard;

  public Board() {
    super();
    super.setLayout(new BorderLayout());

    chessBoard = new JPanel();
    chessBoard.setLayout(new GridLayout(COLS,ROWS));

    // Set up JPanels on bottom and right to display letters and numbers for the board
    // JPanels are called south and west
    super.add(chessBoard, BorderLayout.CENTER);
    super.add(south, BorderLayout.SOUTH);
    super.add(west, BorderLayout.WEST);

    for (int i=0; i<COLS; i++) {
      for (int j=0; j<ROWS; j++) {
        // Set up the grid
        board[i][j] = new JPanel();
        board[i][j].setBackground(getColor(i,j));
        chessBoard.add(board[i][j]);
      }
    }
    super.validate();
  }

  private Color getColor(int x, int y) {
    if ((x + y) % 2 == 0) {
      return Constants.GOLD;
    } else {
      return Constants.PURPLE;
    }
  }

  public void addPiece(Piece piece) {
    JLabel p = piece.getImage();

    board[piece.getX()][piece.getY()].add(p);
    chessBoard.validate();
  }
}

Piece is an interface that that I'm going to use for all my pieces. I've set up the interface and set up one class that implements the interface (Checker class). I have all of that set up. The pieces are JLabels with ImageIcons in them. The only problem I'm having so far is writing a move method. I can figure out the logic make sure a move is a valid one, I just don't know how to actually make the move happen.

EDIT: I'm not even asking about mouse listeners or anything like that, I just want some pseudocode to explain making a piece move from one spot in the array to another.

EDIT 2: Here's the code for my Checkers class.

public class Checker implements Piece {
  private int side,xPos,yPos; 
  private JLabel img;

  public Checker(int team, int x, int y) {
    BufferedImage image;

    try {
      if (team == 0)
        image = ImageIO.read(new File("img/RedPiece.png"));
      else
        image = ImageIO.read(new File("img/BlackPiece.png"));
    } catch(IOException e) {
      image = null;
      System.out.printf("Image file wasn't found!!!");
      System.exit(1);
    }

    img = new JLabel(new ImageIcon(image), SwingConstants.CENTER);
    img.setVerticalAlignment(SwingConstants.CENTER);

    xPos = x;
    yPos = y;
  }

  // TODO Figure out move method
  public void move(int dx, int dy) {

  }

  // Also typical gets and sets for instance variables

So my thought is I call the move method for a checkers piece and, assuming I'm moving from the bottom of the screen to the top it would be piece.move(-1,1); and I have to remove the piece from it's current position, then it's new position in the array is [x + dx][y + dy]

Adam Liss · Accepted Answer · 2012-03-01 03:19:00Z

1

Can you use something like this:

public void movePiece(Piece piece, int dx, int dy) {
  // Save current position, so we can erase the piece.
  int oldX = piece.getX();
  int oldY = piece.getY();

  // Update the location.
  piece.setX(oldX + dx);
  piece.setY(oldY + dy);

  // Remove piece from old position
  board[oldX][oldY].clear();

  // Add it to the new position.
  addPiece(piece);
}

You'd probably want to use a Point instead of individual x and y coordinates; I just thought this would be easier to understand.

answered Mar 1, 2012 at 3:19

Adam Liss

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1 Comment

CaldwellYSR Over a year ago

So this happens in the board class instead of in the individual pieces! That makes alot more sense.

safarisoul · Accepted Answer · 2012-03-01 03:51:24Z

By moving a Piece, you are going to change at least 2 elements of the 2-dimensional array board[][], which is inside your Board class. It's better to implement the method in the Board class, since Piece can only make change to it self. If you put move() in Piece class, and a Piece need to change another Piece, it needs to talk to the Board and ask the Board to pass the reference of the other Piece to it. What are you going to change about each Piece is totally depends on your design, such as colour, picture. Here is my suggestion:

Board:

move(Piece from, Piece to){
   ... // validation
   from.remove();
   to.put(team);
   // over is the one you jump over, optional, some if statements here
   Piece over = Board.getOver(Piece from, Piece to);
   over.remove();
   // check for further move is also optional
   if(board.isFurthermoveAvailable(to)){
      from = to;
      to = board.getFurthermoveLocation(from);
      board.move(from, to);
   }
}
getOver(Piece from, Piece to){
   return board[(from.getX()+to.getX())/2][(from.getY()+to.getY())/2];
}
isFurthermoveAvailable(Piece from){
   int team = from.getTeam();
   ... // your logic
}
// depends on what you return by isFurthermoveAvailable(Piece from)
// if you return boolean, then you also need the method below
// or, you can let the above method return null or a Piece
getFurthermoveLocation(Piece from){
   ... // your logic
}

Piece:

remove(){
   ... // changes such as the picture, colour
}
put(int Team){ // this method is obviously depends on team
   ... 
}
// other methods may assist to the process
getTeam(){
}
getX(){
}
getY(){
}

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