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Thread: Chess

  1. #1
    Junior Member fireredlink5000's Avatar
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    Default 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) )


  2. #2
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    Default Re: Chess

    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.

  3. The Following User Says Thank You to jashburn For This Useful Post:

    fireredlink5000 (May 22nd, 2014)

  4. #3
    Junior Member fireredlink5000's Avatar
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    Default Re: Chess

    Thanks a lot jashburn!

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