Re: How to: referencing variables using the contents of otehr variables.

Joshua Cranmer <Pidgeot18@verizon.invalid>
Wed, 15 Apr 2009 10:42:36 -0400
<gs4ros$jks$> wrote:

OK, my chessboard is represented by an 8x8 char array, call it posn[]
[]. each cell contains one char, which corresponds to FEN notation. an
empty square is '1'. A White King is 'K", a black king is 'k', and so

The best implementation for this would probably be to use an enum:

enum ChessPiece {
   Pawn('P'), Rook('R'), Bishop('B'), Knight('N'), Queen('Q'),

   private char representation;
   ChessPiece(char rep) { representation = rep; }
   public char getNotation() { return representation; }
   public String toString() { return ""+representation; }

public class ChessGame {
   private ChessPiece position[][] = new ChessPiece[8][8];

/* etc. */

In my program, a move is described by a starting an ending pair. In
having the program build a list of legal moves, I start by examining
each cell in the position array, looking for either uppercase or
lowercase letters depending on if it is white's turn or black's turn.

Using enum bodies, this is much, much easier:
public class Position {
   // normal class with rank + file, etc.
   // Probably ought to be immutable

enum ChessPiece {
   Pawn('P') {
     public List<Position> getMoves(Position pos, boolean isBlack,
                                    GameBoard board) {
       List<Position> possibleMoves = new ArrayList<Position>(3);
       Position naturalMove = new Position(pos.getFile(),
          pos.getRank() + (isBlack ? -1 : 1));
       if (!board.isOccupied(naturalMove))
       if (pos.getFile() > 0) {
         Position capture = new Position(pos.getFile() - 1);
         if (board.isOccupied(capture))
       if (pos.getFile() < 7) {
         Position capture = new Position(pos.getFile() + 1);
         if (board.isOccupied(capture))
       // Yes, I know I forgot en passant.
       return possibleMoves;
   // And the other five pieces

   public abstract List<Position> getMoves(Position pos, boolean isBlack,
     GameBoard board);

  OK the select statement is not bad, and I want to keep the data
structure simple. It is more of an academic question really. Is there
some kind of built in JAVA reference function which would eliminate
the need for a switch statement?

A lot of switch statements can be replaced with careful implementation
of polymorphism. In this case, you'd be replacing it with enums
representing the information of specific types.

Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth

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