抽象类与斯卡拉

Question

构造函数的参数我有以下的类模型：

sealed abstract class Tile(val coordinate: Int, val isOccupied: Boolean) { 
    def isEmpty() : Boolean 
    def getPiece() : Option[Piece] 
} 

case class EmptyTile(coordinate: Int) extends Tile(coordinate, false) { 
    override def toString: String = "" +coordinate 
    override def isEmpty() = true 
    override def getPiece() = None 
} 

case class OccupiedTile(coordinate: Int, val piece: Piece) extends Tile(coordinate, true) { 
    override def toString = piece.toString 
    override def isEmpty = false 
    override def getPiece = Some(piece) 
} 

，我得到以下错误：

Error:(6, 22) overriding value coordinate in class Tile of type Int; 
value coordinate needs `override' modifier 
case class EmptyTile(coordinate: Int) extends Tile(coordinate, false) { 
       ^

我在做什么错？

编辑：请求看片类，添加在这里：

import Alliance.Alliance 
import PieceType.PieceType 

abstract class Piece(val piecePosition: Int, val pieceType : PieceType, val alliance: Alliance) extends Movable { 
} 

object PieceType extends Enumeration { 
    type PieceType = Value 
    val PAWN, KNIGHT, BISHOP, ROOK, QUEEN, KING = Value 
} 

Answer 1

你的抽象类Tile声明val coordinate，使得该值可公开访问的。你的案例类别EmptyTile隐含地声明coordinate也是一个值（案例类“魔术”）。基本上，你的case类有效地试图覆盖你的抽象类已经提供的值。

您可以删除抽象类声明中的val，也可以不删除EmptyTile和OccupiedTile个案类。

编辑：评论后提出的备选：

trait Tile { 
    def coordinate: Int 
    def isOccupied: Boolean 
    def isEmpty() : Boolean = !isOccupied 
    def getPiece() : Option[Piece] 
} 

case class EmptyTile(coordinate: Int) extends Tile { 
    override def toString: String = "" +coordinate 
    val isOccupied = false 
    def getPiece() = None 
} 

case class OccupiedTile(coordinate: Int, val piece: Piece) extends Tile { 
    override def toString = piece.toString 
    val isOccupied = true 
    def getPiece = Some(piece) 
} 

Answer 2

case class会自动将其参数val秒。这就是为什么参数coordinate到EmptyTile（理解为val coordinate）与抽象类的val coordinate冲突的原因。

修复此问题的一种方法是将coordinate和isOccupied定义为在Tile中的摘要。 Tile甚至可以是一个特性，而不是一个抽象类：

sealed trait Tile { 
    def coordinate: Int 
    def isOccupied: Boolean 
    ... 
} 

case class EmptyTile(coordinate: Int) extends Tile { 
    def isOccupied = false 
    ... 
} 

case class OccupiedTile(coordinate: Int, piece: Piece) extends Tile { 
    def isOccupied = true 
    ... 
}