Fixed memory leak, improved copy constructors

- Changed unit test package structure to match src
- Refactored PositionTest
+ TestToString method in PositionTest

.classpath

@@ -7,11 +7,7 @@
 			<attribute name="test" value="true"/>
 		</attributes>
 	</classpathentry>
-	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER">
-		<attributes>
-			<attribute name="module" value="true"/>
-		</attributes>
-	</classpathentry>
 	<classpathentry kind="con" path="org.eclipse.jdt.junit.JUNIT_CONTAINER/5"/>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8"/>
 	<classpathentry kind="output" path="bin"/>
 </classpath>

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

@@ -5,7 +5,7 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
-import dev.kske.chess.board.Log.LoggedMove;
+import dev.kske.chess.board.Log.MoveNode;
 import dev.kske.chess.board.Piece.Color;
 import dev.kske.chess.board.Piece.Type;
 
@@ -15,12 +15,12 @@ import dev.kske.chess.board.Piece.Type;
  * Created: <strong>01.07.2019</strong><br>
  * Author: <strong>Kai S. K. Engelbart</strong>
  */
-public class Board implements Cloneable {
+public class Board {
 
-	private Piece[][]						boardArr;
-	private Map<Color, Position>			kingPos;
-	private Map<Color, Map<Type, Boolean>>	castlingRights;
-	private Log								log;
+	private Piece[][]						boardArr		= new Piece[8][8];
+	private Map<Color, Position>			kingPos			= new HashMap<>();
+	private Map<Color, Map<Type, Boolean>>	castlingRights	= new HashMap<>();
+	private Log								log				= new Log();
 
 	private static final Map<Type, int[][]> positionScores;
 
@@ -59,12 +59,44 @@ public class Board implements Cloneable {
 						new int[] { 0, 1, 1, -2, -2, 1, 1, 0 }, new int[] { 0, 0, 0, 0, 0, 0, 0, 0 } });
 	}
 
+	/**
+	 * Initializes the board with the default chess starting position.
+	 */
 	public Board() {
-		boardArr		= new Piece[8][8];
-		kingPos			= new HashMap<>();
-		castlingRights	= new HashMap<>();
-		log				= new Log();
-		initializeDefaultPositions();
+		initDefaultPositions();
+	}
+
+	/**
+	 * Initializes the board with data from a FEN-string.
+	 * 
+	 * @param fen The FEN-string to initialize the board from
+	 */
+	public Board(String fen) {
+		initFromFEN(fen);
+	}
+
+	/**
+	 * Creates a copy of another {@link Board} instance.<br>
+	 * The created object is a deep copy, but does not contain any move history
+	 * apart from the current {@link MoveNode}.
+	 * 
+	 * @param other The {@link Board} instance to copy
+	 */
+	public Board(Board other) {
+		boardArr = new Piece[8][8];
+		for (int i = 0; i < 8; i++)
+			for (int j = 0; j < 8; j++) {
+				if (other.boardArr[i][j] == null) continue;
+				boardArr[i][j]			= (Piece) other.boardArr[i][j].clone();
+				boardArr[i][j].board	= this;
+			}
+
+		kingPos.putAll(other.kingPos);
+		Map<Type, Boolean> whiteCastling = new HashMap<>(other.castlingRights.get(Color.WHITE)),
+				blackCastling = new HashMap<>(other.castlingRights.get(Color.BLACK));
+		castlingRights.put(Color.WHITE, whiteCastling);
+		castlingRights.put(Color.BLACK, blackCastling);
+		log = new Log(other.log, false);
 	}
 
 	/**
@@ -97,7 +129,6 @@ public class Board implements Cloneable {
 	 * Moves a piece across the board without checking if the move is legal.
 	 * 
 	 * @param move The move to execute
-	 * @return The captures piece, or null if the move's destination was empty
 	 */
 	public void move(Move move) {
 		Piece	piece			= getPos(move);
@@ -156,9 +187,9 @@ public class Board implements Cloneable {
 	 * Reverts the last move.
 	 */
 	public void revert() {
-		LoggedMove	loggedMove		= log.getLast();
-		Move		move			= loggedMove.move;
-		Piece		capturedPiece	= loggedMove.capturedPiece;
+		MoveNode	moveNode		= log.getLast();
+		Move		move			= moveNode.move;
+		Piece		capturedPiece	= moveNode.capturedPiece;
 
 		switch (move.type) {
 			case PAWN_PROMOTION:
@@ -327,7 +358,7 @@ public class Board implements Cloneable {
 	/**
 	 * Initialized the board array with the default chess pieces and positions.
 	 */
-	public void initializeDefaultPositions() {
+	public void initDefaultPositions() {
 		// Initialize pawns
 		for (int i = 0; i < 8; i++) {
 			boardArr[i][1]	= new Pawn(Color.BLACK, this);
@@ -370,7 +401,6 @@ public class Board implements Cloneable {
 				boardArr[i][j] = null;
 
 		// Initialize castling rights
-		castlingRights.clear();
 		Map<Type, Boolean> whiteCastling = new HashMap<>(), blackCastling = new HashMap<>();
 		whiteCastling.put(Type.KING, true);
 		whiteCastling.put(Type.QUEEN, true);
@@ -383,34 +413,90 @@ public class Board implements Cloneable {
 	}
 
 	/**
-	 * @return A new instance of this class with a shallow copy of both
-	 *         {@code kingPos} and {code boardArr}
+	 * Initialized the board with a position specified in a FEN-encoded string.
+	 * 
+	 * @param fen The FEN-encoded string representing target state of the board
 	 */
-	@Override
-	public Object clone() {
-		Board board = null;
-		try {
-			board = (Board) super.clone();
-		} catch (CloneNotSupportedException ex) {
-			ex.printStackTrace();
-		}
-		board.boardArr = new Piece[8][8];
-		for (int i = 0; i < 8; i++)
-			for (int j = 0; j < 8; j++) {
-				if (boardArr[i][j] == null) continue;
-				board.boardArr[i][j]		= (Piece) boardArr[i][j].clone();
-				board.boardArr[i][j].board	= board;
+	public void initFromFEN(String fen) {
+		String[] parts = fen.split(" ");
+		log.reset();
+
+		// Piece placement (from white's perspective)
+		String[] rows = parts[0].split("/");
+		for (int i = 0; i < 8; i++) {
+			char[] places = rows[i].toCharArray();
+			for (int j = 0, k = 0; k < places.length; j++, k++) {
+				if (Character.isDigit(places[k])) {
+					for (int l = j; l < Character.digit(places[k], 10); l++, j++)
+						boardArr[j][i] = null;
+					--j;
+				} else {
+					Color color = Character.isUpperCase(places[k]) ? Color.WHITE : Color.BLACK;
+					switch (Character.toLowerCase(places[k])) {
+						case 'k':
+							boardArr[j][i] = new King(color, this);
+							kingPos.put(color, new Position(j, i));
+							break;
+						case 'q':
+							boardArr[j][i] = new Queen(color, this);
+							break;
+						case 'r':
+							boardArr[j][i] = new Rook(color, this);
+							break;
+						case 'n':
+							boardArr[j][i] = new Knight(color, this);
+							break;
+						case 'b':
+							boardArr[j][i] = new Bishop(color, this);
+							break;
+						case 'p':
+							boardArr[j][i] = new Pawn(color, this);
+							break;
+						default:
+							System.err.printf("Unknown character '%c' in board declaration of FEN string '%s'%n",
+									places[k],
+									fen);
+					}
+				}
 			}
+		}
 
-		board.kingPos = new HashMap<>();
-		board.kingPos.putAll(kingPos);
-		board.log = (Log) log.clone();
+		// Active color
+		log.setActiveColor(Color.fromFirstChar(parts[1].charAt(0)));
 
-		return board;
+		// Castling rights
+		Map<Type, Boolean> whiteCastling = new HashMap<>(), blackCastling = new HashMap<>();
+		for (char c : parts[2].toCharArray())
+			switch (c) {
+				case 'K':
+					whiteCastling.put(Type.KING, true);
+				case 'Q':
+					whiteCastling.put(Type.QUEEN, true);
+				case 'k':
+					blackCastling.put(Type.KING, true);
+				case 'q':
+					blackCastling.put(Type.QUEEN, true);
+				case '-':
+					break;
+				default:
+					System.err
+						.printf("Unknown character '%c' in castling rights declaration of FEN string '%s'", c, fen);
+			}
+		castlingRights.put(Color.WHITE, whiteCastling);
+		castlingRights.put(Color.BLACK, blackCastling);
+
+		// En passant availability
+		if (!parts[3].equals("-")) log.setEnPassant(Position.fromSAN(parts[3]));
+
+		// Halfmove clock
+		log.setHalfmoveClock(Integer.parseInt(parts[4]));
+
+		// Fullmove counter
+		log.setFullmoveCounter(Integer.parseInt(parts[5]));
 	}
 
 	/**
-	 * @return A FEN string representing the board
+	 * @return a FEN-encoded string representing the board
 	 */
 	public String toFEN() {
 		StringBuilder sb = new StringBuilder();
@@ -418,39 +504,18 @@ public class Board implements Cloneable {
 		// Piece placement (from white's perspective)
 		for (int i = 0; i < 8; i++) {
 			int emptyCount = 0;
-			for (int j = 0; j < 8; j++)
-				if (boardArr[j][i] == null) ++emptyCount;
+			for (int j = 0; j < 8; j++) {
+				final Piece piece = boardArr[j][i];
+				if (piece == null) ++emptyCount;
 				else {
 					if (emptyCount != 0) {
 						sb.append(emptyCount);
 						emptyCount = 0;
 					}
-					char piece;
-					switch (boardArr[j][i].getType()) {
-						case KING:
-							piece = 'K';
-							break;
-						case QUEEN:
-							piece = 'Q';
-							break;
-						case ROOK:
-							piece = 'R';
-							break;
-						case KNIGHT:
-							piece = 'N';
-							break;
-						case BISHOP:
-							piece = 'B';
-							break;
-						case PAWN:
-							piece = 'P';
-							break;
-						default:
-							piece = '-';
-					}
-					if (boardArr[j][i].getColor() == Color.BLACK) piece = Character.toLowerCase(piece);
-					sb.append(piece);
+					char p = boardArr[j][i].getType().firstChar();
+					sb.append(piece.getColor() == Color.WHITE ? Character.toUpperCase(p) : p);
 				}
+			}
 			if (emptyCount != 0) sb.append(emptyCount);
 			if (i < 7) sb.append('/');
 		}
@@ -458,6 +523,7 @@ public class Board implements Cloneable {
 		// Active color
 		sb.append(" " + log.getActiveColor().firstChar());
 
+		// Castling Rights
 		sb.append(' ');
 		StringBuilder castlingSb = new StringBuilder();
 		if (castlingRights.get(Color.WHITE).get(Type.KING)) castlingSb.append('K');
@@ -467,9 +533,9 @@ public class Board implements Cloneable {
 		if (castlingSb.length() == 0) sb.append("-");
 		sb.append(castlingSb);
 
-		final LoggedMove lastMove = log.getLast();
+		final MoveNode lastMove = log.getLast();
 
-		// En passant availabillity
+		// En passant availability
 		sb.append(" " + (lastMove == null || lastMove.enPassant == null ? "-" : lastMove.enPassant.toSAN()));
 
 		// Halfmove clock
@@ -481,26 +547,56 @@ public class Board implements Cloneable {
 		return sb.toString();
 	}
 
+	/**
+	 * @param pos The position from which to return a piece
+	 * @return The piece at the position
+	 */
 	public Piece get(Position pos) {
 		return boardArr[pos.x][pos.y];
 	}
 
+	/**
+	 * Places a piece at a position.
+	 * 
+	 * @param pos   The position to place the piece at
+	 * @param piece The piece to place
+	 */
 	public void set(Position pos, Piece piece) {
 		boardArr[pos.x][pos.y] = piece;
 	}
 
+	/**
+	 * @param move The move from which position to return a piece
+	 * @return The piece at the position of the move
+	 */
 	public Piece getPos(Move move) {
 		return get(move.pos);
 	}
 
+	/**
+	 * @param move The move from which destination to return a piece
+	 * @return The piece at the destination of the move
+	 */
 	public Piece getDest(Move move) {
 		return get(move.dest);
 	}
 
+	/**
+	 * Places a piece at the position of a move.
+	 * 
+	 * @param move  The move at which position to place the piece
+	 * @param piece The piece to place
+	 */
 	public void setPos(Move move, Piece piece) {
 		set(move.pos, piece);
 	}
 
+	/**
+	 * Places a piece at the destination of a move.
+	 * 
+	 * @param move  The move at which destination to place the piece
+	 * @param piece The piece to place
+	 */
 	public void setDest(Move move, Piece piece) {
 		set(move.dest, piece);
 	}
@@ -511,12 +607,7 @@ public class Board implements Cloneable {
 	public Piece[][] getBoardArr() { return boardArr; }
 
 	/**
-	 * @return The active color for the next move
+	 * @return The move log
 	 */
-	public Color getActiveColor() { return log.getActiveColor(); }
-
-	/**
-	 * @return The current en passant square, or null if there isn't any
-	 */
-	public Position getEnPassantSquare() { return log.getLast() == null ? null : log.getLast().enPassant; }
+	public Log getLog() { return log; }
 }

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

@@ -11,77 +11,190 @@ import dev.kske.chess.board.Piece.Color;
  * Created: <strong>09.07.2019</strong><br>
  * Author: <strong>Kai S. K. Engelbart</strong>
  */
-public class Log implements Cloneable {
+public class Log {
 
-	private List<LoggedMove>	moves;
-	private Color				activeColor;
+	private MoveNode root, current;
+
+	private Position	enPassant;
+	private Color		activeColor;
+	private int			fullmoveCounter, halfmoveClock;
 
 	public Log() {
-		moves		= new ArrayList<>();
-		activeColor	= Color.WHITE;
+		reset();
 	}
 
+	/**
+	 * Creates a (partially deep) copy of another {@link Log} instance which begins
+	 * with the current {@link MoveNode}.
+	 * 
+	 * @param other          The {@link Log} instance to copy
+	 * @param copyVariations If set to {@code true}, subsequent variations of the
+	 *                       current {@link MoveNode} are copied with the
+	 *                       {@link Log}
+	 */
+	public Log(Log other, boolean copyVariations) {
+		enPassant		= other.enPassant;
+		activeColor		= other.activeColor;
+		fullmoveCounter	= other.fullmoveCounter;
+		halfmoveClock	= other.halfmoveClock;
+
+		// The new root is the current node of the copied instance
+		if (!other.isEmpty()) {
+			root		= new MoveNode(other.current, copyVariations);
+			root.parent	= null;
+			current		= root;
+		}
+	}
+
+	/**
+	 * Adds a move to the move history and adjusts the log to the new position.
+	 * 
+	 * @param move          The move to log
+	 * @param capturedPiece The piece captured with the move
+	 * @param pawnMove      {@code true} if the move was made by a pawn
+	 */
 	public void add(Move move, Piece capturedPiece, boolean pawnMove) {
-		// En passant availability
-		Position enPassant = null;
-		if (pawnMove && move.yDist == 2) enPassant = new Position(move.pos.x, move.pos.y + move.ySign);
-
-		// Fullmove counter and halfmove clock
-		int fullmoveCounter, halfmoveClock;
-		if (moves.isEmpty()) {
-			fullmoveCounter	= 1;
-			halfmoveClock	= 0;
-		} else {
-			fullmoveCounter = getLast().fullmoveCounter;
-			if (activeColor == Color.BLACK) ++fullmoveCounter;
-			halfmoveClock = capturedPiece != null || pawnMove ? 0 : getLast().halfmoveClock + 1;
-		}
+		enPassant = pawnMove && move.yDist == 2 ? new Position(move.pos.x, move.pos.y + move.ySign) : null;
+		if (activeColor == Color.BLACK) ++fullmoveCounter;
+		if (pawnMove || capturedPiece != null) halfmoveClock = 0;
+		else++halfmoveClock;
 		activeColor = activeColor.opposite();
-		moves.add(new LoggedMove(move, capturedPiece, enPassant, fullmoveCounter, halfmoveClock));
+		final MoveNode leaf = new MoveNode(move, capturedPiece, enPassant, activeColor, fullmoveCounter, halfmoveClock);
+
+		if (isEmpty()) {
+			root	= leaf;
+			current	= leaf;
+		} else {
+			current.addVariation(leaf);
+			current = leaf;
+		}
 	}
 
-	public LoggedMove getLast() { return moves.isEmpty() ? null : moves.get(moves.size() - 1); }
-
+	/**
+	 * Removed the last move from the log and adjusts its state to the previous
+	 * move.
+	 */
 	public void removeLast() {
-		if (!moves.isEmpty()) {
-			activeColor = activeColor.opposite();
-			moves.remove(moves.size() - 1);
-		}
+		if (!isEmpty() && current.parent != null) {
+			current.parent.variations.remove(current);
+			current			= current.parent;
+			activeColor		= current.activeColor;
+			enPassant		= current.enPassant;
+			fullmoveCounter	= current.fullmoveCounter;
+			halfmoveClock	= current.halfmoveClock;
+		} else reset();
 	}
 
+	public boolean isEmpty() { return root == null; }
+
+	/**
+	 * Reverts the log to its initial state corresponding to the default board
+	 * position.
+	 */
 	public void reset() {
-		moves.clear();
-		activeColor = Color.WHITE;
-	}
-	
-	@Override
-	public Object clone() {
-		Log log = null;
-		try {
-			log = (Log) super.clone();
-		} catch (CloneNotSupportedException e) {
-			e.printStackTrace();
-		}
-		log.moves = new ArrayList<>();
-		log.moves.addAll(this.moves);
-		return log;
+		root			= null;
+		current			= null;
+		enPassant		= null;
+		activeColor		= Color.WHITE;
+		fullmoveCounter	= 1;
+		halfmoveClock	= 0;
 	}
 
+	/**
+	 * @return The first logged move, or {@code null} if there is none
+	 */
+	public MoveNode getRoot() { return root; }
+
+	/**
+	 * @return the last logged move, or {@code null} if there is none
+	 */
+	public MoveNode getLast() { return current; }
+
+	public Position getEnPassant() { return enPassant; }
+
+	public void setEnPassant(Position enPassant) { this.enPassant = enPassant; }
+
 	public Color getActiveColor() { return activeColor; }
 
-	public static class LoggedMove {
+	public void setActiveColor(Color activeColor) { this.activeColor = activeColor; }
 
-		public final Move	move;
-		public final Piece	capturedPiece;
+	public int getFullmoveCounter() { return fullmoveCounter; }
+
+	public void setFullmoveCounter(int fullmoveCounter) { this.fullmoveCounter = fullmoveCounter; }
+
+	public int getHalfmoveClock() { return halfmoveClock; }
+
+	public void setHalfmoveClock(int halfmoveClock) { this.halfmoveClock = halfmoveClock; }
+
+	public static class MoveNode {
+
+		public final Move		move;
+		public final Piece		capturedPiece;
 		public final Position	enPassant;
-		public final int	fullmoveCounter, halfmoveClock;
+		public final Color		activeColor;
+		public final int		fullmoveCounter, halfmoveClock;
 
-		public LoggedMove(Move move, Piece capturedPiece, Position enPassant, int fullmoveCounter, int halfmoveClock) {
+		private MoveNode		parent;
+		private List<MoveNode>	variations;
+
+		/**
+		 * Creates a new {@link MoveNode}.
+		 * 
+		 * @param move            The logged {@link Move}
+		 * @param capturedPiece   The {@link Piece} captures by the logged {@link Move}
+		 * @param enPassant       The en passant {@link Position} valid after the logged
+		 *                        {@link Move}, or {@code null} if there is none
+		 * @param activeColor     The {@link Color} active after the logged {@link Move}
+		 * @param fullmoveCounter
+		 * @param halfmoveClock
+		 */
+		public MoveNode(Move move, Piece capturedPiece, Position enPassant, Color activeColor, int fullmoveCounter,
+				int halfmoveClock) {
 			this.move				= move;
 			this.capturedPiece		= capturedPiece;
 			this.enPassant			= enPassant;
+			this.activeColor		= activeColor;
 			this.fullmoveCounter	= fullmoveCounter;
 			this.halfmoveClock		= halfmoveClock;
 		}
+
+		/**
+		 * Creates a (deep) copy of another {@link MoveNode}.
+		 * 
+		 * @param other          The {@link MoveNode} to copy
+		 * @param copyVariations When this is set to {@code true} a deep copy is
+		 *                       created, which
+		 *                       considers subsequent variations
+		 */
+		public MoveNode(MoveNode other, boolean copyVariations) {
+			this(other.move, other.capturedPiece, other.enPassant, other.activeColor, other.fullmoveCounter,
+					other.halfmoveClock);
+			if (copyVariations && other.variations != null) {
+				if (variations == null) variations = new ArrayList<>();
+				other.variations.forEach(variation -> {
+					MoveNode copy = new MoveNode(variation, true);
+					copy.parent = this;
+					variations.add(copy);
+				});
+			}
+		}
+
+		/**
+		 * Adds another {@link MoveNode} as a child node.
+		 * 
+		 * @param variation The {@link MoveNode} to append to this {@link MoveNode}
+		 */
+		public void addVariation(MoveNode variation) {
+			if (variations == null) variations = new ArrayList<>();
+			if (!variations.contains(variation)) {
+				variations.add(variation);
+				variation.parent = this;
+			}
+		}
+
+		/**
+		 * @return A list of all variations associated with this {@link MoveNode}
+		 */
+		public List<MoveNode> getVariations() { return variations; }
 	}
-}
+}

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

@@ -35,6 +35,10 @@ public class Move {
 				Position.fromSAN(move.substring(2)));
 	}
 
+	public String toSAN() {
+		return pos.toSAN() + dest.toSAN();
+	}
+
 	public boolean isHorizontal() { return yDist == 0; }
 
 	public boolean isVertical() { return xDist == 0; }

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

@@ -29,7 +29,7 @@ public class Pawn extends Piece {
 			move.type = Move.Type.PAWN_PROMOTION;
 
 		// Mark the move as en passant if necessary
-		if (strafe && move.dest.equals(board.getEnPassantSquare())) {
+		if (strafe && move.dest.equals(board.getLog().getEnPassant())) {
 			enPassant	= true;
 			move.type	= Move.Type.EN_PASSANT;
 		}
@@ -84,8 +84,8 @@ public class Pawn extends Piece {
 			moves.parallelStream().forEach(m -> m.type = Move.Type.PAWN_PROMOTION);
 
 		// Add en passant move if necessary
-		if (board.getEnPassantSquare() != null) {
-			Move move = new Move(pos, board.getEnPassantSquare(), Move.Type.EN_PASSANT);
+		if (board.getLog().getEnPassant() != null) {
+			Move move = new Move(pos, board.getLog().getEnPassant(), Move.Type.EN_PASSANT);
 			if (move.isDiagonal() && move.xDist == 1) moves.add(move);
 		}
 

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

@@ -85,18 +85,29 @@ public abstract class Piece implements Cloneable {
 	}
 
 	public static enum Type {
-		KING, QUEEN, ROOK, KNIGHT, BISHOP, PAWN
+		KING, QUEEN, ROOK, KNIGHT, BISHOP, PAWN;
+		
+		/**
+		 * @return The first character of this {@link Type} in algebraic notation and lower case
+		 */
+		public char firstChar() {
+			return this == KNIGHT ? 'n' : Character.toLowerCase(this.toString().charAt(0));
+		}
 	}
 
 	public static enum Color {
 		WHITE, BLACK;
 
-		public Color opposite() {
-			return this == WHITE ? BLACK : WHITE;
+		public static Color fromFirstChar(char c) {
+			return Character.toLowerCase(c) == 'w' ? WHITE : BLACK;
 		}
 
 		public char firstChar() {
 			return this == WHITE ? 'w' : 'b';
 		}
+
+		public Color opposite() {
+			return this == WHITE ? BLACK : WHITE;
+		}
 	}
 }

src/dev/kske/chess/event/Event.java

@@ -0,0 +1,15 @@
+package dev.kske.chess.event;
+
+/**
+ * Project: <strong>Chess</strong><br>
+ * File: <strong>Event.java</strong><br>
+ * Created: <strong>7 Aug 2019</strong><br>
+ * Author: <strong>Kai S. K. Engelbart</strong>
+ */
+public interface Event<T> {
+
+	/**
+	 * @return The data associated with the event
+	 */
+	T getData();
+}

src/dev/kske/chess/event/EventBus.java

@@ -0,0 +1,36 @@
+package dev.kske.chess.event;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Project: <strong>Chess</strong><br>
+ * File: <strong>EventBus.java</strong><br>
+ * Created: <strong>7 Aug 2019</strong><br>
+ * Author: <strong>Kai S. K. Engelbart</strong>
+ */
+public class EventBus {
+
+	private List<Subscribable> subscribers;
+
+	private static EventBus instance;
+
+	public static EventBus getInstance() {
+		if (instance == null) instance = new EventBus();
+		return instance;
+	}
+
+	private EventBus() {
+		subscribers = new ArrayList<>();
+	}
+
+	public void register(Subscribable subscribable) {
+		subscribers.add(subscribable);
+	}
+
+	public void dispatch(Event<?> event) {
+		subscribers.stream().filter(e -> e.supports().contains(event.getClass())).forEach(e -> e.handle(event));
+	}
+
+	public List<Subscribable> getSubscribers() { return subscribers; }
+}

src/dev/kske/chess/event/MoveEvent.java

@@ -0,0 +1,21 @@
+package dev.kske.chess.event;
+
+import dev.kske.chess.board.Move;
+
+/**
+ * Project: <strong>Chess</strong><br>
+ * File: <strong>MoveEvent.java</strong><br>
+ * Created: <strong>7 Aug 2019</strong><br>
+ * Author: <strong>Kai S. K. Engelbart</strong>
+ */
+public class MoveEvent implements Event<Move> {
+
+	private final Move move;
+
+	public MoveEvent(Move move) {
+		this.move = move;
+	}
+
+	@Override
+	public Move getData() { return move; }
+}

src/dev/kske/chess/event/Subscribable.java

@@ -0,0 +1,24 @@
+package dev.kske.chess.event;
+
+import java.util.Set;
+
+/**
+ * Project: <strong>Chess</strong><br>
+ * File: <strong>Subscribable.java</strong><br>
+ * Created: <strong>7 Aug 2019</strong><br>
+ * Author: <strong>Kai S. K. Engelbart</strong>
+ */
+public interface Subscribable {
+
+	/**
+	 * Consumes an event dispatched by an event bus.
+	 * 
+	 * @param event The event dispatched by the event bus, only of supported type
+	 */
+	void handle(Event<?> event);
+
+	/**
+	 * @return A set of classes this class is supposed to handle in events
+	 */
+	Set<Class<?>> supports();
+}

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

@@ -9,6 +9,8 @@ import dev.kske.chess.board.Board;
 import dev.kske.chess.board.GameState;
 import dev.kske.chess.board.Move;
 import dev.kske.chess.board.Piece.Color;
+import dev.kske.chess.event.EventBus;
+import dev.kske.chess.event.MoveEvent;
 import dev.kske.chess.game.ai.AIPlayer;
 import dev.kske.chess.ui.BoardComponent;
 import dev.kske.chess.ui.BoardPane;
@@ -24,18 +26,29 @@ import dev.kske.chess.ui.OverlayComponent;
  */
 public class Game {
 
-	private Map<Color, Player>	players;
+	private Map<Color, Player>	players	= new HashMap<>();
 	private Board				board;
 	private OverlayComponent	overlayComponent;
 	private BoardComponent		boardComponent;
 
 	public Game(BoardPane boardPane, String whiteName, String blackName) {
-		players				= new HashMap<>();
 		board				= new Board();
+		init(boardPane, whiteName, blackName);
+	}
+
+	public Game(BoardPane boardPane, String whiteName, String blackName, String fen) {
+		board = new Board(fen);
+		init(boardPane, whiteName, blackName);
+	}
+
+	private void init(BoardPane boardPane, String whiteName, String blackName) {
+
+		// Initialize / synchronize UI
 		overlayComponent	= boardPane.getOverlayComponent();
 		boardComponent		= boardPane.getBoardComponent();
 		boardComponent.setBoard(board);
 
+		// Initialize players
 		players.put(Color.WHITE, getPlayer(whiteName, Color.WHITE));
 		players.put(Color.BLACK, getPlayer(blackName, Color.BLACK));
 
@@ -59,12 +72,17 @@ public class Game {
 
 	public void onMove(Player player, Move move) {
 		if (board.getPos(move).getColor() == player.color && board.attemptMove(move)) {
+
 			// Redraw
 			boardComponent.repaint();
 			overlayComponent.displayArrow(move);
 
+			// Run garbage collection
+			System.gc();
+
 			System.out.printf("%s: %s%n", player.color, move);
 			System.out.println("FEN: " + board.toFEN());
+			EventBus.getInstance().dispatch(new MoveEvent(move));
 			GameState eventType = board.getGameEventType(board.getDest(move).getColor().opposite());
 			switch (eventType) {
 				case CHECKMATE:
@@ -76,30 +94,33 @@ public class Game {
 				case CHECK:
 					System.out.printf("%s in check!%n", player.color.opposite());
 				default:
-					players.get(board.getActiveColor()).requestMove();
+					players.get(board.getLog().getActiveColor()).requestMove();
 			}
 		} else player.requestMove();
 	}
 
 	public void start() {
-		players.get(Color.WHITE).requestMove();
+		players.get(board.getLog().getActiveColor()).requestMove();
 	}
 
 	public void reset() {
 		players.values().forEach(Player::cancelMove);
-		board.initializeDefaultPositions();
+		board.initDefaultPositions();
 		boardComponent.repaint();
 		overlayComponent.clearDots();
 		overlayComponent.clearArrow();
 	}
 
 	/**
-	 * Removed all connections between the game and the UI.
+	 * Stops the game by disconnecting its players form the UI.
 	 */
-	public void disconnect() {
+	public void stop() {
 		players.values().forEach(Player::disconnect);
 	}
 
+	/**
+	 * Assigns the players their opposite colors.
+	 */
 	public void swapColors() {
 		players.values().forEach(Player::cancelMove);
 		Player	white	= players.get(Color.WHITE);
@@ -108,10 +129,16 @@ public class Game {
 		black.setColor(Color.WHITE);
 		players.put(Color.WHITE, black);
 		players.put(Color.BLACK, white);
-		players.get(board.getActiveColor()).requestMove();
+		players.get(board.getLog().getActiveColor()).requestMove();
 	}
 
+	/**
+	 * @return The board on which this game's moves are made
+	 */
 	public Board getBoard() { return board; }
 
+	/**
+	 * @return The players participating in this game
+	 */
 	public Map<Color, Player> getPlayers() { return players; }
 }

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

@@ -56,7 +56,7 @@ public class NaturalPlayer extends Player implements MouseListener {
 			pos = new Position(evt.getPoint().x / overlayComponent.getTileSize(),
 					evt.getPoint().y / overlayComponent.getTileSize());
 
-			Board board = (Board) NaturalPlayer.this.board.clone();
+			Board board = new Board(this.board);
 			if (board.get(pos) != null && board.get(pos).getColor() == color) {
 				List<Position> positions = board.getMoves(pos)
 					.stream()

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

@@ -50,7 +50,7 @@ public class AIPlayer extends Player {
 			/*
 			 * Get a copy of the board and the available moves.
 			 */
-			Board		board	= (Board) AIPlayer.this.board.clone();
+			Board		board	= new Board(this.board);
 			List<Move>	moves	= board.getMoves(color);
 
 			/*
@@ -64,7 +64,7 @@ public class AIPlayer extends Player {
 			for (int i = 0; i < numThreads; i++) {
 				if (rem-- > 0) ++endIndex;
 				endIndex += step;
-				processors.add(new MoveProcessor((Board) board.clone(), moves.subList(beginIndex, endIndex), color,
+				processors.add(new MoveProcessor(new Board(board), moves.subList(beginIndex, endIndex), color,
 						maxDepth, alphaBetaThreshold));
 				beginIndex = endIndex;
 			}

src/dev/kske/chess/uci/UCIListener.java

@@ -81,7 +81,7 @@ public interface UCIListener {
 	/**
 	 * The engine sends information to the GUI.
 	 * 
-	 * @param additionalInfo Contains all pieces of information to be sent
+	 * @param info Contains all pieces of information to be sent
 	 */
 	default void onInfo(UCIInfo info) {}
 

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

@@ -0,0 +1,55 @@
+package dev.kske.chess.ui;
+
+import java.awt.datatransfer.DataFlavor;
+import java.awt.datatransfer.UnsupportedFlavorException;
+import java.awt.dnd.DnDConstants;
+import java.awt.dnd.DropTargetAdapter;
+import java.awt.dnd.DropTargetDropEvent;
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.FileReader;
+import java.io.IOException;
+import java.util.List;
+
+import dev.kske.chess.game.Game;
+
+/**
+ * Project: <strong>Chess</strong><br>
+ * File: <strong>FENDropTarget.java</strong><br>
+ * Created: <strong>13 Aug 2019</strong><br>
+ * Author: <strong>Kai S. K. Engelbart</strong>
+ */
+public class FENDropTarget extends DropTargetAdapter {
+
+	private MainWindow mainWindow;
+
+	public FENDropTarget(MainWindow mainWindow) {
+		this.mainWindow = mainWindow;
+	}
+
+	@SuppressWarnings("unchecked")
+	@Override
+	public void drop(DropTargetDropEvent evt) {
+		try {
+			evt.acceptDrop(DnDConstants.ACTION_COPY_OR_MOVE);
+			((List<File>) evt.getTransferable().getTransferData(DataFlavor.javaFileListFlavor)).forEach(file -> {
+				try (BufferedReader br = new BufferedReader(new FileReader(file))) {
+					final GamePane	gamePane	= mainWindow.addGamePane();
+					final String	fen			= br.readLine();
+					GameConfigurationDialog.show((whiteName, blackName) -> {
+						final Game game = new Game(gamePane.getBoardPane(), whiteName, blackName, fen);
+						gamePane.setGame(game);
+						game.start();
+					});
+					evt.dropComplete(true);
+				} catch (IOException e) {
+					e.printStackTrace();
+					evt.rejectDrop();
+				}
+			});
+		} catch (UnsupportedFlavorException | IOException ex) {
+			ex.printStackTrace();
+			evt.rejectDrop();
+		}
+	}
+}

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

@@ -4,6 +4,7 @@ import java.awt.Font;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.function.BiConsumer;
 
 import javax.swing.DefaultComboBoxModel;
 import javax.swing.JButton;
@@ -17,66 +18,59 @@ import javax.swing.JLabel;
  * Created: <strong>24.07.2019</strong><br>
  * Author: <strong>Kai S. K. Engelbart</strong>
  */
-public class GameConfigurationDialog extends JDialog {
+public class GameConfigurationDialog {
 
-	private static final long serialVersionUID = 9080577278529876972L;
+	private GameConfigurationDialog() {}
 
-	private String	whiteName, blackName;
-	private boolean	startGame;
+	public static void show(BiConsumer<String, String> action) {
+		new JDialog() {
 
-	/**
-	 * Create the dialog.
-	 */
-	public GameConfigurationDialog() {
-		setTitle("Game Configuration");
-		setBounds(100, 100, 281, 142);
-		setModal(true);
-		setLocationRelativeTo(null);
-		getContentPane().setLayout(null);
+			private static final long serialVersionUID = -5768339760489440385L;
 
-		startGame = false;
-		List<String> options = new ArrayList<>(Arrays.asList("Natural Player", "AI Player"));
-		EngineUtil.getEngineInfos().forEach(info -> options.add(info.name));
+			{
+				setTitle("Game Configuration");
+				setBounds(100, 100, 281, 142);
+				setModal(true);
+				setLocationRelativeTo(null);
+				getContentPane().setLayout(null);
 
-		JLabel lblWhite = new JLabel("White:");
-		lblWhite.setFont(new Font("Tahoma", Font.PLAIN, 14));
-		lblWhite.setBounds(10, 11, 49, 14);
-		getContentPane().add(lblWhite);
+				List<String> options = new ArrayList<>(Arrays.asList("Natural Player", "AI Player"));
+				EngineUtil.getEngineInfos().forEach(info -> options.add(info.name));
 
-		JComboBox<Object> cbWhite = new JComboBox<>();
-		cbWhite.setModel(new DefaultComboBoxModel<Object>(options.toArray()));
-		cbWhite.setBounds(98, 9, 159, 22);
-		getContentPane().add(cbWhite);
+				JLabel lblWhite = new JLabel("White:");
+				lblWhite.setFont(new Font("Tahoma", Font.PLAIN, 14));
+				lblWhite.setBounds(10, 11, 49, 14);
+				getContentPane().add(lblWhite);
 
-		JLabel lblBlack = new JLabel("Black:");
-		lblBlack.setFont(new Font("Tahoma", Font.PLAIN, 14));
-		lblBlack.setBounds(10, 38, 49, 14);
-		getContentPane().add(lblBlack);
+				JComboBox<Object> cbWhite = new JComboBox<>();
+				cbWhite.setModel(new DefaultComboBoxModel<Object>(options.toArray()));
+				cbWhite.setBounds(98, 9, 159, 22);
+				getContentPane().add(cbWhite);
 
-		JComboBox<Object> cbBlack = new JComboBox<>();
-		cbBlack.setModel(new DefaultComboBoxModel<Object>(options.toArray()));
-		cbBlack.setBounds(98, 36, 159, 22);
-		getContentPane().add(cbBlack);
+				JLabel lblBlack = new JLabel("Black:");
+				lblBlack.setFont(new Font("Tahoma", Font.PLAIN, 14));
+				lblBlack.setBounds(10, 38, 49, 14);
+				getContentPane().add(lblBlack);
 
-		JButton btnStart = new JButton("Start");
-		btnStart.addActionListener((evt) -> {
-			startGame	= true;
-			whiteName	= options.get(cbWhite.getSelectedIndex());
-			blackName	= options.get(cbBlack.getSelectedIndex());
-			dispose();
-		});
-		btnStart.setBounds(20, 73, 89, 23);
-		getContentPane().add(btnStart);
+				JComboBox<Object> cbBlack = new JComboBox<>();
+				cbBlack.setModel(new DefaultComboBoxModel<Object>(options.toArray()));
+				cbBlack.setBounds(98, 36, 159, 22);
+				getContentPane().add(cbBlack);
 
-		JButton btnCancel = new JButton("Cancel");
-		btnCancel.addActionListener((evt) -> dispose());
-		btnCancel.setBounds(157, 73, 89, 23);
-		getContentPane().add(btnCancel);
+				JButton btnStart = new JButton("Start");
+				btnStart.addActionListener((evt) -> {
+					dispose();
+					action.accept(options.get(cbWhite.getSelectedIndex()), options.get(cbBlack.getSelectedIndex()));
+				});
+				btnStart.setBounds(20, 73, 89, 23);
+				getContentPane().add(btnStart);
+
+				JButton btnCancel = new JButton("Cancel");
+				btnCancel.addActionListener((evt) -> dispose());
+				btnCancel.setBounds(157, 73, 89, 23);
+				getContentPane().add(btnCancel);
+
+			}
+		}.setVisible(true);
 	}
-
-	public String getWhiteName() { return whiteName; }
-
-	public String getBlackName() { return blackName; }
-
-	public boolean isStartGame() { return startGame; }
 }

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

@@ -0,0 +1,126 @@
+package dev.kske.chess.ui;
+
+import java.awt.GridBagConstraints;
+import java.awt.GridBagLayout;
+import java.awt.GridLayout;
+
+import javax.swing.JButton;
+import javax.swing.JComponent;
+import javax.swing.JLabel;
+import javax.swing.JPanel;
+
+import dev.kske.chess.board.Piece.Color;
+import dev.kske.chess.game.Game;
+import dev.kske.chess.game.NaturalPlayer;
+
+/**
+ * Project: <strong>Chess</strong><br>
+ * File: <strong>GamePane.java</strong><br>
+ * Created: <strong>23.08.2019</strong><br>
+ * Author: <strong>Kai S. K. Engelbart</strong>
+ */
+public class GamePane extends JComponent {
+
+	private static final long serialVersionUID = 4349772338239617477L;
+
+	private JButton		btnRestart, btnSwapColors;
+	private BoardPane	boardPane;
+	private LogPanel	logPanel;
+	private Game		game;
+	private Color		activeColor;
+
+	public GamePane() {
+		activeColor = Color.WHITE;
+
+		GridBagLayout gridBagLayout = new GridBagLayout();
+		gridBagLayout.columnWidths	= new int[] { 450, 1, 0 };
+		gridBagLayout.rowHeights	= new int[] { 33, 267, 1, 0 };
+		gridBagLayout.columnWeights	= new double[] { 0.0, 0.0, Double.MIN_VALUE };
+		gridBagLayout.rowWeights	= new double[] { 0.0, 0.0, 0.0, Double.MIN_VALUE };
+		setLayout(gridBagLayout);
+
+		JPanel toolPanel = new JPanel();
+		btnRestart = new JButton("Restart");
+		btnRestart.addActionListener((evt) -> { if (game != null) game.reset(); game.start(); });
+
+		btnSwapColors = new JButton("Play as black");
+		btnSwapColors.addActionListener((evt) -> {
+			game.swapColors();
+			btnSwapColors.setText("Play as " + activeColor.toString().toLowerCase());
+			activeColor = activeColor.opposite();
+		});
+
+		toolPanel.add(btnRestart);
+		toolPanel.add(btnSwapColors);
+
+		GridBagConstraints gbc_toolPanel = new GridBagConstraints();
+		gbc_toolPanel.anchor	= GridBagConstraints.NORTH;
+		gbc_toolPanel.fill		= GridBagConstraints.HORIZONTAL;
+		gbc_toolPanel.gridx		= 0;
+		gbc_toolPanel.gridy		= 0;
+		add(toolPanel, gbc_toolPanel);
+		boardPane = new BoardPane();
+		GridBagConstraints gbc_boardPane = new GridBagConstraints();
+		gbc_boardPane.fill	= GridBagConstraints.BOTH;
+		gbc_boardPane.gridx	= 0;
+		gbc_boardPane.gridy	= 1;
+		add(boardPane, gbc_boardPane);
+
+		JPanel				numberPanel		= new JPanel(new GridLayout(8, 1));
+		GridBagConstraints	gbc_numberPanel	= new GridBagConstraints();
+		gbc_numberPanel.anchor	= GridBagConstraints.WEST;
+		gbc_numberPanel.fill	= GridBagConstraints.VERTICAL;
+		gbc_numberPanel.gridx	= 1;
+		gbc_numberPanel.gridy	= 1;
+		add(numberPanel, gbc_numberPanel);
+
+		JPanel				letterPanel		= new JPanel(new GridLayout(1, 8));
+		GridBagConstraints	gbc_letterPanel	= new GridBagConstraints();
+		gbc_letterPanel.anchor	= GridBagConstraints.NORTH;
+		gbc_letterPanel.fill	= GridBagConstraints.HORIZONTAL;
+		gbc_letterPanel.gridx	= 0;
+		gbc_letterPanel.gridy	= 2;
+		add(letterPanel, gbc_letterPanel);
+
+		// Initialize board coordinates
+		for (int i = 0; i < 8; i++) {
+			numberPanel.add(new JLabel(String.valueOf(8 - i)));
+			JLabel letterLabel = new JLabel(String.valueOf((char) (65 + i)));
+			letterLabel.setHorizontalAlignment(JLabel.CENTER);
+			letterPanel.add(letterLabel);
+		}
+
+		// Initialize LogPanel
+		logPanel = new LogPanel();
+		GridBagConstraints gbc_logPanel = new GridBagConstraints();
+		gbc_logPanel.anchor	= GridBagConstraints.EAST;
+		gbc_logPanel.fill	= GridBagConstraints.VERTICAL;
+		gbc_logPanel.gridx	= 2;
+		gbc_logPanel.gridy	= 1;
+		add(logPanel, gbc_logPanel);
+	}
+
+	/**
+	 * @return The {@link BoardPane} instance associated with this game pane
+	 */
+	public BoardPane getBoardPane() { return boardPane; }
+
+	/**
+	 * @return The {@link Game} instance associated with this game pane
+	 */
+	public Game getGame() { return game; }
+
+	/**
+	 * Assigns a new {@link Game} instance to this game pane. If exactly one of the
+	 * players is natural, color swapping functionality is enabled.
+	 * 
+	 * @param game The {@link Game} to assign to this game pane.
+	 */
+	public void setGame(Game game) {
+		if (this.game != null) this.game.stop();
+		this.game = game;
+		btnSwapColors.setEnabled(game.getPlayers().get(Color.WHITE) instanceof NaturalPlayer
+				^ game.getPlayers().get(Color.BLACK) instanceof NaturalPlayer);
+		logPanel.setLog(game.getBoard().getLog());
+	}
+}

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

@@ -1,47 +0,0 @@
-package dev.kske.chess.ui;
-
-import java.awt.BorderLayout;
-
-import javax.swing.JFrame;
-import javax.swing.JPanel;
-import javax.swing.JTable;
-import javax.swing.border.EmptyBorder;
-import javax.swing.table.DefaultTableModel;
-
-import dev.kske.chess.board.Move;
-
-/**
- * Project: <strong>Chess</strong><br>
- * File: <strong>LogFrame.java</strong><br>
- * Created: <strong>17.07.2019</strong><br>
- * Author: <strong>Kai S. K. Engelbart</strong>
- */
-public class LogFrame extends JFrame {
-
-	private static final long serialVersionUID = 1932671698254197119L;
-
-	private JPanel	mcontentPane;
-	private JTable	mtable;
-
-	/**
-	 * Create the frame.
-	 */
-	public LogFrame() {
-		setTitle("Move History");
-		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
-		setBounds(100, 100, 450, 300);
-		mcontentPane = new JPanel();
-		mcontentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
-		mcontentPane.setLayout(new BorderLayout(0, 0));
-		setContentPane(mcontentPane);
-
-		mtable = new JTable();
-		mtable.setModel(new DefaultTableModel(new Object[][] {}, new String[] { "White", "Black" }));
-		mtable.setEnabled(false);
-		mcontentPane.add(mtable, BorderLayout.CENTER);
-	}
-
-	public void add(Move move) {
-
-	}
-}

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

@@ -0,0 +1,76 @@
+package dev.kske.chess.ui;
+
+import java.awt.BorderLayout;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import javax.swing.JPanel;
+import javax.swing.JScrollPane;
+import javax.swing.JTable;
+import javax.swing.border.EmptyBorder;
+import javax.swing.table.DefaultTableModel;
+
+import dev.kske.chess.board.Log;
+import dev.kske.chess.board.Log.MoveNode;
+import dev.kske.chess.event.Event;
+import dev.kske.chess.event.EventBus;
+import dev.kske.chess.event.MoveEvent;
+import dev.kske.chess.event.Subscribable;
+
+/**
+ * Project: <strong>Chess</strong><br>
+ * File: <strong>LogPanel.java</strong><br>
+ * Created: <strong>17.07.2019</strong><br>
+ * Author: <strong>Kai S. K. Engelbart</strong>
+ */
+public class LogPanel extends JPanel implements Subscribable {
+
+	private static final long serialVersionUID = 1932671698254197119L;
+
+	private JTable	mtable;
+
+	private Log log;
+
+	/**
+	 * Create the frame.
+	 */
+	public LogPanel() {
+		setBorder(new EmptyBorder(5, 5, 5, 5));
+		setLayout(new BorderLayout(0, 0));
+
+		mtable = new JTable();
+		mtable.setEnabled(false);
+		add(new JScrollPane(mtable), BorderLayout.CENTER);
+
+		EventBus.getInstance().register(this);
+	}
+
+	@Override
+	public Set<Class<?>> supports() {
+		return new HashSet<>(Arrays.asList(MoveEvent.class));
+	}
+
+	@Override
+	public void handle(Event<?> event) {
+		if (log == null) return;
+
+		// TODO: Display log with variations
+		final List<MoveNode>	moves	= /* log.getLoggedMoves() */ new ArrayList<>();
+		String[][]				data	= new String[moves.size() / 2 + moves.size() % 2][2];
+		for (int i = 0; i < data.length; i++) {
+			data[i][0] = moves.get(i * 2).move.toSAN();
+			if (i * 2 + 1 < moves.size()) data[i][1] = moves.get(i * 2 + 1).move.toSAN();
+		}
+		mtable.setModel(new DefaultTableModel(data, new String[] { "White", "Black" }));
+	}
+
+	public Log getLog() { return log; }
+
+	public void setLog(Log log) {
+		this.log = log;
+		handle(null);
+	}
+}

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

@@ -1,18 +1,11 @@
 package dev.kske.chess.ui;
 
-import java.awt.BorderLayout;
 import java.awt.EventQueue;
-import java.awt.GridLayout;
 import java.awt.Toolkit;
+import java.awt.dnd.DropTarget;
 
-import javax.swing.JButton;
 import javax.swing.JFrame;
-import javax.swing.JLabel;
-import javax.swing.JPanel;
-
-import dev.kske.chess.board.Piece.Color;
-import dev.kske.chess.game.Game;
-import dev.kske.chess.game.NaturalPlayer;
+import javax.swing.JTabbedPane;
 
 /**
  * Project: <strong>Chess</strong><br>
@@ -20,27 +13,21 @@ import dev.kske.chess.game.NaturalPlayer;
  * Created: <strong>01.07.2019</strong><br>
  * Author: <strong>Kai S. K. Engelbart</strong>
  */
-public class MainWindow {
+public class MainWindow extends JFrame {
 
-	private JFrame		mframe;
-	private JButton		btnRestart, btnSwapColors;
-	private BoardPane	boardPane;
-	private Game		game;
-	private Color		activeColor;
+	private static final long serialVersionUID = -3100939302567978977L;
+
+	private JTabbedPane tabbedPane;
 
 	/**
 	 * Launch the application.
 	 */
 	public static void main(String[] args) {
-		EventQueue.invokeLater(new Runnable() {
-
-			public void run() {
-				try {
-					MainWindow window = new MainWindow();
-					window.mframe.setVisible(true);
-				} catch (Exception e) {
-					e.printStackTrace();
-				}
+		EventQueue.invokeLater(() -> {
+			try {
+				new MainWindow();
+			} catch (Exception ex) {
+				ex.printStackTrace();
 			}
 		});
 	}
@@ -49,6 +36,7 @@ public class MainWindow {
 	 * Create the application.
 	 */
 	public MainWindow() {
+		super("Chess by Kai S. K. Engelbart");
 		initialize();
 	}
 
@@ -56,58 +44,48 @@ public class MainWindow {
 	 * Initialize the contents of the frame.
 	 */
 	private void initialize() {
-		mframe = new JFrame("Chess by Kai S. K. Engelbart");
-		mframe.setResizable(false);
-		mframe.setBounds(100, 100, 494, 565);
-		mframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
-		mframe.setIconImage(Toolkit.getDefaultToolkit().getImage(getClass().getResource("/pieces/queen_white.png")));
+		// Configure frame
+		setResizable(false);
+		setBounds(100, 100, 494, 565);
+		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+		setIconImage(Toolkit.getDefaultToolkit().getImage(getClass().getResource("/pieces/queen_white.png")));
 
-		boardPane = new BoardPane();
-		mframe.getContentPane().add(boardPane, BorderLayout.CENTER);
+		// Add frame content
+		tabbedPane = new JTabbedPane();
+		getContentPane().add(tabbedPane);
 
-		JPanel toolPanel = new JPanel();
-		btnRestart = new JButton("Restart");
-		btnRestart.addActionListener((evt) -> { if (game != null) game.reset(); game.start(); });
+		setJMenuBar(new MenuBar(this));
+		new DropTarget(this, new FENDropTarget(this));
 
-		activeColor		= Color.WHITE;
-		btnSwapColors	= new JButton("Play as black");
-		btnSwapColors.addActionListener((evt) -> {
-			game.swapColors();
-			btnSwapColors.setText("Play as " + activeColor.toString().toLowerCase());
-			activeColor = activeColor.opposite();
-		});
-
-		toolPanel.add(btnRestart);
-		toolPanel.add(btnSwapColors);
-		mframe.getContentPane().add(toolPanel, BorderLayout.NORTH);
-
-		JPanel letterPanel = new JPanel(new GridLayout(1, 8));
-		for (int i = 0; i < 8; i++) {
-			JLabel letterLabel = new JLabel(String.valueOf((char) (65 + i)));
-			letterLabel.setHorizontalAlignment(JLabel.CENTER);
-			letterPanel.add(letterLabel);
-		}
-		mframe.add(letterPanel, BorderLayout.SOUTH);
-
-		JPanel numberPanel = new JPanel(new GridLayout(8, 1));
-		for (int i = 0; i < 8; i++)
-			numberPanel.add(new JLabel(String.valueOf(8 - i)));
-		mframe.add(numberPanel, BorderLayout.EAST);
-
-		mframe.setJMenuBar(new MenuBar(this));
-
-		mframe.pack();
-		mframe.setLocationRelativeTo(null);
+		// Update position and dimensions
+		pack();
+		setLocationRelativeTo(null);
+		setVisible(true);
 	}
 
-	public BoardPane getBoardPane() { return boardPane; }
+	/**
+	 * @return The currently selected {@link GamePane} component
+	 */
+	public GamePane getSelectedGamePane() { return (GamePane) tabbedPane.getSelectedComponent(); }
 
-	public Game getGame() { return game; }
+	/**
+	 * Creates a new {@link GamePane}, adds it to the tabbed pane and opens it.
+	 * 
+	 * @return The new {@link GamePane}
+	 */
+	public GamePane addGamePane() {
+		GamePane gamePane = new GamePane();
+		tabbedPane.add("Game " + (tabbedPane.getComponentCount() + 1), gamePane);
+		tabbedPane.setSelectedIndex(tabbedPane.getComponentCount() - 1);
+		return gamePane;
+	}
 
-	public void setGame(Game game) {
-		if (this.game != null) this.game.disconnect();
-		this.game = game;
-		btnSwapColors.setEnabled(game.getPlayers().get(Color.WHITE) instanceof NaturalPlayer
-				^ game.getPlayers().get(Color.BLACK) instanceof NaturalPlayer);
+	/**
+	 * Removes a {@link GamePane} form the tabbed pane.
+	 * 
+	 * @param index The index of the {@link GamePane} to remove
+	 */
+	public void removeGamePane(int index) {
+		tabbedPane.remove(index);
 	}
 }

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

@@ -20,12 +20,10 @@ public class MenuBar extends JMenuBar {
 
 	private static final long serialVersionUID = -7221583703531248228L;
 
-	private final MainWindow	mainWindow;
-	private final BoardPane		boardPane;
+	private final MainWindow mainWindow;
 
 	public MenuBar(MainWindow mainWindow) {
-		this.mainWindow	= mainWindow;
-		boardPane		= mainWindow.getBoardPane();
+		this.mainWindow = mainWindow;
 
 		initGameMenu();
 		initEngineMenu();
@@ -36,16 +34,16 @@ public class MenuBar extends JMenuBar {
 		JMenu		gameMenu		= new JMenu("Game");
 		JMenuItem	newGameMenuItem	= new JMenuItem("New Game");
 		newGameMenuItem.addActionListener((evt) -> {
-			GameConfigurationDialog dialog = new GameConfigurationDialog();
-			dialog.setVisible(true);
-			if (dialog.isStartGame()) startGame(new Game(boardPane, dialog.getWhiteName(), dialog.getBlackName()));
+			GameConfigurationDialog.show((whiteName, blackName) -> {
+				GamePane	gamePane	= mainWindow.addGamePane();
+				Game		game		= new Game(gamePane.getBoardPane(), whiteName, blackName);
+				gamePane.setGame(game);
+				game.start();
+			});
 		});
 		gameMenu.add(newGameMenuItem);
-
 		add(gameMenu);
-
-		// Start a game
-		startGame(new Game(boardPane, "Natural Player", "Natural Player"));
+		newGameMenuItem.doClick();
 	}
 
 	private void initEngineMenu() {
@@ -71,19 +69,25 @@ public class MenuBar extends JMenuBar {
 		JMenu toolsMenu = new JMenu("Tools");
 
 		JMenuItem exportFENMenuItem = new JMenuItem("Export board to FEN");
-		exportFENMenuItem.addActionListener((evt) -> Toolkit.getDefaultToolkit()
-			.getSystemClipboard()
-			.setContents(new StringSelection(mainWindow.getGame().getBoard().toFEN()), null));
+		exportFENMenuItem.addActionListener((evt) -> {
+			final String fen = mainWindow.getSelectedGamePane().getGame().getBoard().toFEN();
+			Toolkit.getDefaultToolkit().getSystemClipboard().setContents(new StringSelection(fen), null);
+			JOptionPane.showMessageDialog(mainWindow, String.format("FEN-string copied to clipboard!%n%s", fen));
+		});
 		toolsMenu.add(exportFENMenuItem);
 
+		JMenuItem loadFromFENMenuItem = new JMenuItem("Load board from FEN");
+		loadFromFENMenuItem.addActionListener((evt) -> {
+			final GamePane	gamePane	= mainWindow.addGamePane();
+			final String	fen			= JOptionPane.showInputDialog("Enter a FEN string: ");
+			GameConfigurationDialog.show((whiteName, blackName) -> {
+				final Game game = new Game(gamePane.getBoardPane(), whiteName, blackName, fen);
+				gamePane.setGame(game);
+				game.start();
+			});
+		});
+		toolsMenu.add(loadFromFENMenuItem);
+
 		add(toolsMenu);
 	}
-
-	private void startGame(Game game) {
-		mainWindow.setGame(game);
-
-		// Update board and board component
-		game.reset();
-		game.start();
-	}
 }

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

@@ -19,11 +19,9 @@ import dev.kske.chess.board.Piece;
  */
 public class TextureUtil {
 
-	private static Map<String, Image> textures, scaledTextures;
+	private static Map<String, Image> textures = new HashMap<>(), scaledTextures = new HashMap<>();
 
 	static {
-		textures = new HashMap<>();
-		scaledTextures	= new HashMap<>();
 		loadPieceTextures();
 		scaledTextures.putAll(textures);
 	}

test/dev/kske/chess/board/BoardTest.java

@@ -1,4 +1,4 @@
-package dev.kske.chess.test;
+package dev.kske.chess.board;
 
 import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertNotSame;
@@ -6,10 +6,7 @@ import static org.junit.Assert.assertNotSame;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
-import dev.kske.chess.board.Board;
-import dev.kske.chess.board.Move;
 import dev.kske.chess.board.Piece.Color;
-import dev.kske.chess.board.Queen;
 
 /**
  * Project: <strong>Chess</strong><br>
@@ -34,13 +31,13 @@ class BoardTest {
 	 */
 	@Test
 	void testClone() {
-		Board clone = (Board) board.clone();
+		Board clone = new Board(board);
 		assertNotSame(clone, board);
 		assertNotSame(clone.getBoardArr(), board.getBoardArr());
 
 		clone.getBoardArr()[0][0] = new Queen(Color.BLACK, clone);
 		clone.move(new Move(1, 1, 1, 2));
 		assertNotEquals(clone.getBoardArr()[0][0], board.getBoardArr()[0][0]);
-		assertNotEquals(clone.getActiveColor(), board.getActiveColor());
+		assertNotEquals(clone.getLog().getActiveColor(), board.getLog().getActiveColor());
 	}
 }

test/dev/kske/chess/board/LogTest.java

@@ -0,0 +1,165 @@
+package dev.kske.chess.board;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import org.junit.jupiter.api.Test;
+
+import dev.kske.chess.board.Piece.Color;
+
+/**
+ * Project: <strong>Chess</strong><br>
+ * File: <strong>LogTest.java</strong><br>
+ * Created: <strong>13 Sep 2019</strong><br>
+ * Author: <strong>Kai S. K. Engelbart</strong>
+ */
+class LogTest {
+
+	Log log = new Log();
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#Log()}.
+	 */
+	@Test
+	void testLog() {
+		assertTrue(log.isEmpty());
+		assertNull(log.getLast());
+		assertNull(log.getRoot());
+		assertEquals(log.getActiveColor(), Color.WHITE);
+		assertNull(log.getEnPassant());
+		assertEquals(log.getFullmoveCounter(), 1);
+		assertEquals(log.getHalfmoveClock(), 0);
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#clone()}.
+	 */
+	@Test
+	void testClone() {
+		Log other = new Log(log, false);
+		log.setActiveColor(Color.WHITE);
+		other.setActiveColor(Color.BLACK);
+		assertNotEquals(log.getActiveColor(), other.getActiveColor());
+		log.add(Move.fromSAN("a2a4"), null, true);
+		log.add(Move.fromSAN("a4a5"), null, true);
+		other.add(Move.fromSAN("a2a4"), null, true);
+		other.add(Move.fromSAN("a4a5"), null, true);
+		assertNotEquals(log.getRoot(), other.getRoot());
+		assertNotEquals(log.getRoot().getVariations(), other.getRoot().getVariations());
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#add(dev.kske.chess.board.Move, dev.kske.chess.board.Piece, boolean)}.
+	 */
+	@Test
+	void testAdd() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#removeLast()}.
+	 */
+	@Test
+	void testRemoveLast() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#isEmpty()}.
+	 */
+	@Test
+	void testIsEmpty() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#reset()}.
+	 */
+	@Test
+	void testReset() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#getRoot()}.
+	 */
+	@Test
+	void testGetRoot() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#getLast()}.
+	 */
+	@Test
+	void testGetLast() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#getEnPassant()}.
+	 */
+	@Test
+	void testGetEnPassant() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#setEnPassant(dev.kske.chess.board.Position)}.
+	 */
+	@Test
+	void testSetEnPassant() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#getActiveColor()}.
+	 */
+	@Test
+	void testGetActiveColor() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#setActiveColor(dev.kske.chess.board.Piece.Color)}.
+	 */
+	@Test
+	void testSetActiveColor() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#getFullmoveCounter()}.
+	 */
+	@Test
+	void testGetFullmoveCounter() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#setFullmoveCounter(int)}.
+	 */
+	@Test
+	void testSetFullmoveCounter() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#getHalfmoveClock()}.
+	 */
+	@Test
+	void testGetHalfmoveClock() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Log#setHalfmoveClock(int)}.
+	 */
+	@Test
+	void testSetHalfmoveClock() {
+		fail("Not yet implemented");
+	}
+}

test/dev/kske/chess/board/PositionTest.java

@@ -0,0 +1,47 @@
+package dev.kske.chess.board;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Project: <strong>Chess</strong><br>
+ * File: <strong>PositionTest.java</strong><br>
+ * Created: <strong>24.07.2019</strong><br>
+ * Author: <strong>Kai S. K. Engelbart</strong>
+ */
+class PositionTest {
+
+	final int	n			= 4;
+	Position[]	positions	= new Position[] { new Position(0, 0), new Position(7, 7), new Position(0, 7), new Position(7, 0) };
+	String[]	sans		= new String[] { "a8", "h1", "a1", "h8" };
+	String[]	strings		= new String[] { "[0, 0]", "[7, 7]", "[0, 7]", "[7, 0]" };
+
+	/**
+	 * Test method for
+	 * {@link dev.kske.chess.board.Position#fromSAN(java.lang.String)}.
+	 */
+	@Test
+	void testFromSAN() {
+		for (int i = 0; i < n; i++)
+			assertEquals(positions[i], Position.fromSAN(sans[i]));
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Position#toSAN()}.
+	 */
+	@Test
+	void testToSAN() {
+		for (int i = 0; i < n; i++)
+			assertEquals(sans[i], positions[i].toSAN());
+	}
+
+	/**
+	 * Test method for {@link dev.kske.chess.board.Position#toString()}.
+	 */
+	@Test
+	void testToString() {
+		for (int i = 0; i < n; i++)
+			assertEquals(strings[i], positions[i].toString());
+	}
+}

test/dev/kske/chess/test/PositionTest.java

@@ -1,52 +0,0 @@
-package dev.kske.chess.test;
-
-import static org.junit.Assert.assertEquals;
-
-import java.util.Arrays;
-import java.util.List;
-import java.util.stream.IntStream;
-
-import org.junit.jupiter.api.BeforeEach;
-import org.junit.jupiter.api.Test;
-
-import dev.kske.chess.board.Position;
-
-/**
- * Project: <strong>Chess</strong><br>
- * File: <strong>PositionTest.java</strong><br>
- * Created: <strong>24.07.2019</strong><br>
- * Author: <strong>Kai S. K. Engelbart</strong>
- */
-class PositionTest {
-
-	List<Position>	positions;
-	List<String>	sans;
-
-	/**
-	 * @throws java.lang.Exception
-	 */
-	@BeforeEach
-	void setUp() throws Exception {
-		positions	= Arrays.asList(new Position(0, 0), new Position(7, 7), new Position(0, 7), new Position(7, 0));
-		sans		= Arrays.asList("a8", "h1", "a1", "h8");
-	}
-
-	/**
-	 * Test method for
-	 * {@link dev.kske.chess.board.Position#fromSAN(java.lang.String)}.
-	 */
-	@Test
-	void testFromSAN() {
-		IntStream.range(0, positions.size())
-			.forEach(i -> assertEquals(positions.get(i), Position.fromSAN(sans.get(i))));
-	}
-
-	/**
-	 * Test method for {@link dev.kske.chess.board.Position#toSAN()}.
-	 */
-	@Test
-	void testToSAN() {
-		IntStream.range(0, positions.size()).forEach(i -> assertEquals(sans.get(i), positions.get(i).toSAN()));
-	}
-
-}