Thread: Chess

Hey guys, I'm writing Chess Program for fun. I hit a road block. I wondering if guys can see what is wrong with it. Here is the basic code.

public class Piece {
 
	/**
	 * The Piece's Row.
	 */
	private int row;
 
	/**
	 * The Piece's Column.
	 */
	private int column;
 
	/**
	 * The Piece's Color.
	 */
	private final boolean isWhite;
 
	/**
	 * Piece's Constructor
	 * @param row The Piece's Row.
	 * @param column The Piece's Column.
	 * @param isWhite The Piece's Color.
	 */
	public Piece(int row, int column, final boolean isWhite){
		this.row = row;
		this.column = column;
		this.isWhite = isWhite;
	}
 
	/**
	 * @return The Piece's Row.
	 */
	public int getRow(){
		return this.row;
	}
 
	/**
	 * @return The Piece's Column.
	 */
	public int getColumn(){
		return this.column;
	}
 
	/**
	 * @return true == isWhite. Otherwise false.
	 */
	public boolean isWhite(){
		return this.isWhite;
	}
 
	/**
	 * The Piece moving to a square.
	 * @param row The Square's Row.
	 * @param column The Square's Column.
	 * @return true when the move is successful. Otherwise false.
	 */
	public boolean moveTo(int row, int column){
		return false;
	}
 
	@Override
	public String toString(){
		if(this.isWhite){
			return "w";
		}
		return "b";
	}
}

public interface Rook {
 
	/**
	 * The Rook moving to a square.
	 * @param row The Square's Row.
	 * @param column The Square's Column.
	 * @return true when the move is successful. Otherwise false.
	 */
	public boolean moveTo(int row, int column);
 
	/**
	 * The movement of the Rook.
	 */
	public void moveLikeARook();
}

public interface Bishop {
 
	/**
	 * The Bishop moving to a square.
	 * @param row The Square's Row.
	 * @param column The Square's Column.
	 * @return true when the move is successful. Otherwise false.
	 */
	public boolean moveTo(int row, int column);
 
	/**
	 * The movement of the Bishop.
	 */
	public void moveLikeABishop();
}

public class Queen extends Piece implements Bishop, Rook{	
	/**
	 * Queen's Constructor. 
	 * @param row The Queen's Row.
	 * @param column The Queen's Column.
	 * @param isWhite The Queen's Cololr.
	 */
	public Queen(int row, int column, boolean isWhite) {
		super(row, column, isWhite);
	}
 
	@Override
	public void moveLikeARook() {
		System.out.println("Move Like A Rook");
	}
 
	@Override
	public void moveLikeABishop() {
		System.out.println("Move Like A Bishop");
	}
 
	@Override
	public boolean moveTo(int row, int column) {
		System.out.println("moveTo");
		if(this instanceof Bishop){
			System.out.println("It's a Bishop!");
		}else if(this instanceof Rook){
			System.out.println("It's a Rook!");
		}else if(this instanceof Queen){
			System.out.println("It's a Queen!");
		}
		return false;
	}
 
	public String toString(){
		if(this instanceof Bishop){
			return super.toString() + "B";
		}else if(this instanceof Rook){
			return super.toString() + "R";
		}
		return super.toString() + "Q";
	}
}

Now this is my issue. For this class:

/**
 * 
 * @author Anthony Wong
 *
 */
public final class Chess {
	protected static Piece[][] chessBoard = new Piece[7][7];
 
	public static void main(String[] args) {
		Bishop bishop1 = new Queen(1,2,true);
		chessBoard[0][0] = (Piece) bishop1;
		Piece piece = chessBoard[0][0];
		piece.moveTo(1, 1);
 
		Rook rook1 = new Queen(1, 2, true);
		chessBoard[1][1] = (Piece)rook1;
		Piece piece2 = chessBoard[1][1];
		piece2.moveTo(1, 2);
	}
}

When I run the code, this is my output:
moveTo
It's a Bishop!
moveTo
It's a Bishop!

How come this is my output? (i.e. line: piece.moveTo(1,1); && piece2.moveTo(1,2) )

There are 3 main points:

1. bishop1 is assigned the reference to a Queen object, which is then assigned to piece; rook1 is also assigned the reference to a Queen object, which is then assigned to piece2
2. Queen implements Bishop and Rook
3. (Most important point) "The instanceof operator compares an object to a specified type. You can use it to test if an object is an instance of a class, an instance of a subclass, or an instance of a class that implements a particular interface." (Source: Equality, Relational, and Conditional Operators (The Java™ Tutorials > Learning the Java Language > Language Basics))

Since Queen implements Bishop, and "instanceof Bishop" is the first test in the moveTo() method, this is why it prints "It's a Bishop!"

This will become even clearer if you go through the example in the link above.

Thanks a lot jashburn!