remove "instanceof Pawn"

app/src/main/java/chess/model/ChessBoard.java

@@ -103,7 +103,7 @@ public class ChessBoard {
 			for (int j = 0; j < Coordinate.VALUE_MAX; j++) {
 				Coordinate coordinate = new Coordinate(i, j);
 				Piece piece = pieceAt(coordinate);
-				if (piece != null && kingIdentifier.visit(piece)) {
+				if (kingIdentifier.isKing(piece)) {
 					return coordinate;
 				}
 			}

app/src/main/java/chess/model/Game.java

@@ -1,6 +1,6 @@
 package chess.model;
 
-import chess.model.pieces.Pawn;
+import chess.model.visitor.PawnIdentifier;
 
 public class Game {
 	private final ChessBoard board;
@@ -66,15 +66,15 @@ public class Game {
 	 */
 	private Coordinate pawnPromotePosition(Color color) {
 		int enemyLineY = color == Color.White ? 0 : 7;
+		PawnIdentifier identifier = new PawnIdentifier(color);
 
 		for (int x = 0; x < Coordinate.VALUE_MAX; x++) {
 			Coordinate pieceCoords = new Coordinate(x, enemyLineY);
 			Piece piece = getBoard().pieceAt(pieceCoords);
 
-			if (piece == null || !(piece instanceof Pawn) || piece.getColor() != color)
-				continue;
+			if (identifier.isPawn(piece))
+				return pieceCoords;
 
-			return pieceCoords;
 		}
 
 		return null;

app/src/main/java/chess/model/visitor/KingIdentifier.java

@@ -1,6 +1,7 @@
 package chess.model.visitor;
 
 import chess.model.Color;
+import chess.model.Piece;
 import chess.model.PieceVisitor;
 import chess.model.pieces.*;
 
@@ -12,6 +13,12 @@ public class KingIdentifier implements PieceVisitor<Boolean> {
 		this.color = color;
 	}
 
+	public boolean isKing(Piece piece) {
+		if (piece == null)
+			return false;
+		return visit(piece);
+	}
+
 	@Override
 	public Boolean visitPiece(Bishop bishop) {
 		return false;

app/src/main/java/chess/model/visitor/PawnIdentifier.java

@@ -0,0 +1,52 @@
+package chess.model.visitor;
+
+import chess.model.Color;
+import chess.model.Piece;
+import chess.model.PieceVisitor;
+import chess.model.pieces.*;
+
+public class PawnIdentifier implements PieceVisitor<Boolean> {
+
+	private final Color color;
+
+	public PawnIdentifier(Color color) {
+		this.color = color;
+	}
+
+	public boolean isPawn(Piece piece) {
+		if (piece == null)
+			return false;
+		return visit(piece);
+	}
+
+	@Override
+	public Boolean visitPiece(Bishop bishop) {
+		return false;
+	}
+
+	@Override
+	public Boolean visitPiece(King king) {
+		return false;
+	}
+
+	@Override
+	public Boolean visitPiece(Knight knight) {
+		return false;
+	}
+
+	@Override
+	public Boolean visitPiece(Pawn pawn) {
+		return pawn.getColor() == color;
+	}
+
+	@Override
+	public Boolean visitPiece(Queen queen) {
+		return false;
+	}
+
+	@Override
+	public Boolean visitPiece(Rook rook) {
+		return false;
+	}
+
+}