Added simple (yet surprisingly effective) AI player

+ AIPlayer class
+ Evaluation method in Board
+ AI vs AI button in GameModeDialog (produces a rendering delay)

src/dev/kske/chess/board/Board.java

@@ -131,6 +131,36 @@ public class Board {
 				: getMoves(color).isEmpty() ? GameEventType.STALEMATE : GameEventType.NONE;
 	}
 
+	/**
+	 * Evaluated the board.
+	 * 
+	 * @param color The color to evaluate for
+	 * @return An positive number representing how good the position is
+	 */
+	public int evaluate(Color color) {
+		int score = 0;
+		for (int i = 0; i < 8; i++)
+			for (int j = 0; j < 8; j++)
+				if (boardArr[i][j] != null && boardArr[i][j].getColor() == color) switch (boardArr[i][j].getType()) {
+					case QUEEN:
+						score += 8;
+						break;
+					case ROOK:
+						score += 5;
+						break;
+					case KNIGHT:
+						score += 3;
+						break;
+					case BISHOP:
+						score += 3;
+						break;
+					case PAWN:
+						score += 1;
+						break;
+				}
+		return score;
+	}
+
 	public void registerGameEventListener(GameEventListener listener) {
 		gameEventListeners.add(listener);
 	}

src/dev/kske/chess/game/AIPlayer.java

@@ -0,0 +1,47 @@
+package dev.kske.chess.game;
+
+import dev.kske.chess.board.Board;
+import dev.kske.chess.board.Move;
+import dev.kske.chess.board.Piece;
+import dev.kske.chess.board.Piece.Color;
+
+/**
+ * Project: <strong>Chess</strong><br>
+ * File: <strong>AIPlayer.java</strong><br>
+ * Created: <strong>06.07.2019</strong><br>
+ * Author: <strong>Kai S. K. Engelbart</strong>
+ */
+public class AIPlayer extends Player {
+
+	private Move bestMove;
+
+	public AIPlayer(Board board, Color color) {
+		super(board, color);
+	}
+
+	@Override
+	public void requestMove() {
+		findBestMove(board, color, 0);
+		game.onMove(this, bestMove);
+	}
+
+	private int findBestMove(Board board, Color color, int depth) {
+		int bestValue = Integer.MIN_VALUE;
+		for (Move move : board.getMoves(color)) {
+			Piece	capturePiece	= board.move(move);
+			int		teamValue		= board.evaluate(color);
+			int		enemyValue		= board.evaluate(color.opposite());
+			int		valueChange		= teamValue - enemyValue;
+
+			if (depth < 4) valueChange -= findBestMove(board, color.opposite(), depth + 1);
+
+			if (valueChange > bestValue) {
+				bestValue = valueChange;
+				if (depth == 0) bestMove = move;
+			}
+
+			board.revert(move, capturePiece);
+		}
+		return bestValue;
+	}
+}

src/dev/kske/chess/game/Game.java

@@ -5,6 +5,7 @@ import java.util.Map;
 import dev.kske.chess.board.Board;
 import dev.kske.chess.board.Move;
 import dev.kske.chess.board.Piece.Color;
+import dev.kske.chess.ui.BoardPanel;
 
 /**
  * Project: <strong>Chess</strong><br>
@@ -16,10 +17,12 @@ public class Game {
 
 	private Map<Color, Player>	players;
 	private Board				board;
+	private BoardPanel			boardPanel;
 
-	public Game(Map<Color, Player> players, Board board) {
+	public Game(Map<Color, Player> players, Board board, BoardPanel boardPanel) {
 		this.players	= players;
 		this.board		= board;
+		this.boardPanel	= boardPanel;
 
 		// Initialize the game variable in each player
 		players.values().forEach(player -> player.setGame(this));
@@ -32,6 +35,7 @@ public class Game {
 	public void onMove(Player player, Move move) {
 		if (board.getPos(move).getColor() == player.color && board.attemptMove(move)) {
 			System.out.printf("%s: %s%n", player.color, move);
+			boardPanel.repaint();
 			players.get(player.color.opposite()).requestMove();
 		} else {
 			System.out.printf("%s: Illegal move!%n", player.getColor());

src/dev/kske/chess/ui/GameModeDialog.java

@@ -8,6 +8,7 @@ import javax.swing.JButton;
 import javax.swing.JDialog;
 
 import dev.kske.chess.board.Piece.Color;
+import dev.kske.chess.game.AIPlayer;
 import dev.kske.chess.game.Game;
 import dev.kske.chess.game.NaturalPlayer;
 import dev.kske.chess.game.Player;
@@ -29,7 +30,7 @@ public class GameModeDialog extends JDialog {
 		super();
 		setModal(true);
 		setTitle("Game Mode Selection");
-		setBounds(100, 100, 231, 99);
+		setBounds(100, 100, 231, 133);
 		setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
 		getContentPane().setLayout(new FlowLayout(FlowLayout.CENTER, 5, 5));
 
@@ -38,12 +39,29 @@ public class GameModeDialog extends JDialog {
 			Map<Color, Player> players = new HashMap<>();
 			players.put(Color.WHITE, new NaturalPlayer(boardPanel.getBoard(), Color.WHITE, boardPanel));
 			players.put(Color.BLACK, new NaturalPlayer(boardPanel.getBoard(), Color.BLACK, boardPanel));
-			new Game(players, boardPanel.getBoard()).start();
+			new Game(players, boardPanel.getBoard(), boardPanel).start();
 			dispose();
 		});
 		getContentPane().add(btnNatural);
 
 		JButton btnAI = new JButton("Game against AI");
+		btnAI.addActionListener((evt) -> {
+			Map<Color, Player> players = new HashMap<>();
+			players.put(Color.WHITE, new NaturalPlayer(boardPanel.getBoard(), Color.WHITE, boardPanel));
+			players.put(Color.BLACK, new AIPlayer(boardPanel.getBoard(), Color.BLACK));
+			new Game(players, boardPanel.getBoard(), boardPanel).start();
+			dispose();
+		});
 		getContentPane().add(btnAI);
+
+		JButton btnAI2 = new JButton("AI against AI");
+		btnAI2.addActionListener((evt) -> {
+			Map<Color, Player> players = new HashMap<>();
+			players.put(Color.WHITE, new AIPlayer(boardPanel.getBoard(), Color.WHITE));
+			players.put(Color.BLACK, new AIPlayer(boardPanel.getBoard(), Color.BLACK));
+			new Game(players, boardPanel.getBoard(), boardPanel).start();
+			dispose();
+		});
+		getContentPane().add(btnAI2);
 	}
 }