CODEWITHSUNDEEP
javaoop
Matt
Matt

Reputation: 11317

How do I define a constructor for all subclasses

I'm making a chess game and each Piece has a subclass - King, Queen, Rook etc

Each Piece has a playerId attribute which I want to set like this:

public abstract class Piece {

    private int playerId;

    public Piece(int playerId) {
        this.playerId = playerId;
    }
}

But this only works if I instantiate Piece directly (which I can't anyway, because it's abstract). Is there a way to make this constructor apply to ALL subclasses, without having to manually implement it in each class?

Upvotes: 1

Views: 227

Answers (4)

Qwerky
Qwerky

Reputation: 18435

You might want to think about static factory methods.

public abstract class Piece
{
  private int playerId;

  public int getPlayerId()
  {
    return playerId;
  }

  public int setPlayerId(int playerId)
  {
    this.playerId = playerId;
  }
}

public class King extends Piece
{
  //King specific stuff in here
}

public class ChessFactory
{
  public static King newKing(int id)
  {
    King king = new King();
    king.setId(id);
    return king;
  }
}

Upvotes: 1

Buhake Sindi
Buhake Sindi

Reputation: 89169

One way (The way I usually do this) is to have a protected piece constructor

public abstract class Piece {

    private int playerId;

    protected Piece(int playerId) {
        this.playerId = playerId;
    }
}

and for every subpiece, e.g. Rook

public class Rook extends Piece {

    public Rook(int playerId) {
        super(playerId);
    }
}

That way, the constructor for Piece is indeed to everyone except its descendants.

Upvotes: 0

Petar Minchev
Petar Minchev

Reputation: 47373

There is no easy way. In each of the descendants write something like this:

public Rook(int playerId) {
    super(playerId);
}

Upvotes: 1

Peter Lawrey
Peter Lawrey

Reputation: 533492

Usually, your IDE can do this for you. When you extend Piece it should offer to add all the constructors you need. It still needs to be done, but avoids having to do it manually.

Perhaps you can avoid sub-classing Piece by making seperating its behaviour from the Pieces.

enum PieceType {
  KING, QUEEN, ROOK;
}

public class Piece {
  private final PieceType pieceType;
  private final String playerId;
  public Piece ... // one constructor for all.
}

Upvotes: 1

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