Implementing Rook logic in multidimensional array

Question

I have a question that I have been trying to figure out, but I am stuck. Basically I have been trying to implement the logic of a rook's movement in a game that's not chess, but I'm stuck on it. I'll give you the details:

• The Board is a 5x5 multidimensional array where there are only pawns and rooks for each player
• The goal is to capture all your opponent's pieces and the one that captures them all will win the game.
• Rooks can move as far as they want in one direction, until they hit something blocking their path.

The thing my rook does right now is that it can go one direction but it can go anywhere in that line. I need help on trying to figure out how to add more logic to make sure it can only go as long as the path is clear. Here is an example:

The small "p" and "r" are player 2's pieces and the big "P" and "R" are player one's pieces. Right now the top-right R (rook) can only move right, but if you do that it will go beyond the pawns, and then can go as far down as it wants.

* R R R *
* P P P *
* * * * *
* p p p *
* r r r *

Here is the code for what I have for the rook:

public boolean isLegalMove(Location from,Location to)
{
  // Row is XPosition (Up/Down)
  // Column is YPosition(Left/Right)

  int fromRow = from.getXPosition();
  int fromColumn = from.getYPosition();
  int toRow = to.getXPosition();
  int toColumn = to.getYPosition();

  // higher row or column or both
  if(((fromColumn >= toColumn) || (fromColumn <= toColumn)) && ((fromRow == toRow))) {
    return true;
  }
  if(((fromRow >= toRow) || (fromRow <= toRow)) && ((fromColumn == toColumn))) {
    return true;
  }
  return false; 
}

I guess I'm going to make another method to check the logics if there's any thing in the path, calling it isPathClear()

EDIT:
Here's the rest of the code:

 public class Board
  {
    // The depth and width of the field.
    public static final int ROW = 5;
    public static final int COLUMN = 5;
    public static final String EMPTYPIECE = " * ";

     //Storage for the game pieces
     private GamePiece [] [] gameBoard;
     //Makes the balls and torches for player1
     private Pawn1 p1Pawn1,p1Pawn2,p1Pawn3;
     private Rook1 p1Rook1,p1Rook2,p1Rook3;

     //Makes the ball and torchers for player2
     private Pawn2 p2Pawn1,p2Pawn2,p2Pawn3;
     private Rook2 p2Rook1,p2Rook2,p1Rook3;

/**
 * Makes a 5x5 Gameboard
 */
public Board()
{
    // initialise instance variables
    gameBoard = new GamePiece [ROW][COLUMN];

    //Makes pieces for player1
    p1Pawn1 = new Pawn1();
    p1Pawn2 = new Pawn1();
    p1Pawn3 = new Pawn1();
    p1Rook1 = new Rook1();
    p1Rook2 = new Rook1();
    p1Rook3 = new Rook1();

    //Makes pieces for player2
    p2Pawn1 = new Pawn2();
    p2Pawn2 = new Pawn2();
    p2Pawn3 = new Pawn2();
    p2Rook1 = new Rook2();
    p2Rook2 = new Rook2();
    p2Rook3 = new Rook2();
}

/**
 * Makes new games
 */
public void newGame()
{  
    // Assigns the piece of the board for player1
    gameBoard[0][1] = p1Rook1;
    gameBoard[0][2] = p1Rook2;
    gameBoard[0][3] = p1Rook3;
    gameBoard[1][1] = p1Pawn1;
    gameBoard[1][2] = p1Pawn2;
    gameBoard[1][3] = p1Pawn3;

    // Assigns the pieces of the board for player2
    gameBoard[4][1] = p2Rook1;
    gameBoard[4][2] = p2Rook2;
    gameBoard[4][3] = p2Rook3;
    gameBoard[3][1] = p2Pawn1;
    gameBoard[3][2] = p2Pawn2;
    gameBoard[3][3] = p2Pawn3;
}

/**
 * Displays the content of the board
 */
public void displayBoard()
{
    System.out.println("  a  b  c  d  e");
    int counter = 1;
    for (int i = 0; i < gameBoard.length; i++){
       System.out.print(counter);
       for (int j = 0; j < gameBoard[i].length; j++) {
           if (gameBoard[i][j] == null) {
              System.out.print(EMPTYPIECE);
           } else {
               System.out.print(" " + gameBoard[i][j] + " ");
           }
       }
       counter++;
       System.out.println();
    }
}

/**
 * Moves the movepiece from one locatin to another
 * @param from - where the location was from
 * @param to - Where the location is going to
 */
public void movePiece(Location from,Location to) throws InvalidMoveException
{
    int fromRow     = from.getXPosition();
    int fromColumn  = from.getYPosition();
    int toRow       = to.getXPosition();
    int toColumn    = to.getYPosition();

    if (gameBoard[fromRow][fromColumn] == null) {
        throw new InvalidMoveException("Invalid input for source location.");
    }
    if (! checkBounds(from, to)) {
        throw new InvalidMoveException("Invalid input for destination location.");
    }
    if (isSameLocation(from, to)){
        throw new InvalidMoveException("Invalid move, source and destination cannot    bethe same.");
    }
    if (! gameBoard[fromRow][fromColumn].isLegalMove(from, to)) {
        throw new InvalidMoveException("Invalid move for this piece.");
    }
       gameBoard[toRow][toColumn] = gameBoard[fromRow][fromColumn];
       gameBoard[fromRow][fromColumn] = null;

   displayBoard();
}

/**
 * Checks a proposed move to ensure it is within the bounds of the board.
 * @param source location, destination location
 * @return true if both source and destination are within bounds
 */
private boolean checkBounds(Location from, Location to)
{
    int fromRow     = from.getXPosition();
    int fromColumn  = from.getYPosition();
    int toRow       = to.getXPosition();
    int toColumn    = to.getYPosition();

    boolean testFrom = (fromRow >= 0) && (fromColumn >= 0) && (fromRow < gameBoard.length) && (fromColumn < gameBoard[0].length);
    boolean testTo = (toRow >= 0) && (toColumn >= 0) && (toRow < gameBoard.length) && (toColumn < gameBoard[0].length);
    return testFrom && testTo;
}

/**
 * Checks a proposed move to ensure source and destination are different.
 * @param source location, destination location
 * @return true if source and destination are the same
 */
private boolean isSameLocation(Location from, Location to)
{
    int fromRow     = from.getXPosition();
    int fromColumn  = from.getYPosition();
    int toRow       = to.getXPosition();
    int toColumn    = to.getYPosition();
    return fromRow == toRow && fromColumn == toColumn;
}

Answer 1

You can't know if the path is clear without knowing what else is on the board. However, your method signature doesn't give this function access to the layout of the board. If you pass the entire board, you can use a loop to check all the squares in between for other pieces.

---

From Lord Torgamus:

You wouldn't check to see if the board is null. You'd have to check the individual spaces between the rook's source and destination locations.

---

Now that I know what board looks like, here's some code:

public boolean isLegalMove(Location from,Location to)
{
  // Row is XPosition (Up/Down)
  // Column is YPosition(Left/Right)

  int fromRow = from.getXPosition();
  int fromColumn = from.getYPosition();
  int toRow = to.getXPosition();
  int toColumn = to.getYPosition();

  // Has to be same row or column
  if(fromRow != toRow || fromColumn != toColumn) return false;
  // Can't move to the same square
  if(fromRow == toRow && fromColumn == toColumn) return false;

  // Rows are the same
  if(fromRow - toRow == 0) {
    // this will hold the column of the we're going to check next
    int newPos = fromColumn;
    // Should we go up or down?
    int amount = (toColumn - fromColumn < 0) ? -1 : 1;
    while(newPos != toColumn) {
      newPos += amount;
      // if it's not null, we found a different piece
      if(gameBoard[fromRow][newPos] != null) return false;
    }
    if(gameBoard[toRow][toColumn] != null) {
      // return false if it's your own piece, true if it's not
    }
  // Columns are the same
  } else {
    // this will hold the row of the we're going to check next
    int newPos = fromRow;
    // Should we go up or down?
    int amount = (toRow - fromRow < 0) ? -1 : 1;
    while(newPos != toRow) {
      newPos += amount;
      // if it's not null, we found a different piece
      if(gameBoard[newPos][fromColumn] != null) return false;
    }
    if(gameBoard[toRow][toColumn] != null) {
      // return false if it's your own piece, true if it's not
    }
  }

  return true;
}

---

Edited for the case where you want to be able to capture an opponent's piece... but I didn't put the last bit of code in because you have to change the method signature again. Look for my comment. Notice also it's a while loop now, not a do-while.