Method undefined for the Type Piece problem

Question

I've been working on a project of coding chess in Java. I have an abstract class named Piece which has one abstract method and a couple of normal methods. I also have a class for each chess piece, and they all extend Piece.

There is a class the represents the board called Board as well. In this class, I have a method that checks if the piece at a given position belongs to the other player or not. In this method I call a method from the Piece class that gets the color called getColor(). when I call this method on a piece it says "The method getColor() is undefined for the type Piece" even though it is a method that is created inside the Piece class. I really don't know what to do to solve this issue.

Here's the Piece class code:

abstract class Piece {
    private Color color;

    /**
     * @param color the color of the piece.
     */
    public Piece(Color color) {
        this.color = color;
    }

    /**
     * This method gives a list of all legal moves a piece at a given position in a
     * given board can do.
     * 
     * @param position the position of the piece in the board.
     * @param board    the board in which the piece is in.
     * @return a list of all legal moves.
     */
    abstract List<Position> getPossibleMoves(Position position, Board board);


    /**
     * @return the color of the piece.
     */
    public Color getColor() {
        return color;
    }

Here's the Board class code:

public class Board {
    private Square[][] square;

    /**
     * Initialises an 8 by 8 squares 2d table.
     */
    public Board() {
        this.square = new Square[8][8];
        for (int row = 0; row < square.length; row++) {
            for (int column = 0; column < square.length; column++) {
                square[row][column] = new Square<>(null);
            }
        }
    } 

     /**
     * This method sets the given piece in the given position in the board.
     * Throw an exception if the position is not in the board.
     * 
     * @param piece    The piece to be set.
     * @param position The position to set the piece in.
     */
    public <Piece> void setPiece(Piece piece, Position position) {
        if (piece instanceof Piece) {
            if (contains(position)) {
                square[position.getRow()][position.getColumn()].setPiece(piece);
            } else {
                throw new IllegalArgumentException("The given position isn't part of the board :" + position);
            }
        }
    }

    /**
     * This method returns the piece that is in the given position in the board.
     * Throws an exception if the position is not in the board.
     * 
     * @param pos The position of the piece in the board.
     * @return the piece.
     */
    public <Piece> Piece getPiece(Position pos) {
        Piece piece;
        if (contains(pos)) {
            piece = (Piece) square[pos.getRow()][pos.getColumn()].getPiece();
        } else {
            throw new IllegalArgumentException("The given position isn't part of the board :" + pos);
        }
        return piece;
    }
     /**
     * This method determines whether or not the piece at the given position has the
     * same or the opposite color as the given color.
     * throws an exception if position is not in the board.
     * 
     * @param pos the position of the piece to be checked.
     * @param col the color to check if the piece is in the opposite color or not.
     * @return true if the piece is in the opposite color, false otherwise.
     */
    public <Piece> boolean containsOppositeColor(Position pos, Color col) {
        boolean containsOpposite = false;
        if (contains(pos)) {
            if (!isFree(pos)) {
                Piece piece = getPiece(pos);
                containsOpposite = (col.opposite() == piece.getColor());
            }
        } else {
            throw new IllegalArgumentException("The given position isn't part of the board :" + pos);
        }
        return containsOpposite;
    }

The problem is at the line that says : containsOpposite = (col.opposite() == piece.getColor());

Answer 1

The problem is you define a generic type <Piece> in a lot of the methods in Board. This hides the actual type Piece and replaces it with an unknown type basically equivalent to Object, which doesn't have a getColor method. You need to remove all the occurrences of the generic type <Piece> in the methods of Board.

So, for example

public <Piece> Piece getPiece(Position pos)

should be

public Piece getPiece(Position pos)

And the same goes for the other methods:

public <Piece> void setPiece(Piece piece, Position position)

should be

public void setPiece(Piece piece, Position position)

and

public <Piece> boolean containsOppositeColor(Position pos, Color col)

should be

public boolean containsOppositeColor(Position pos, Color col)