Basic game works except for deliberately introduced bug

src/main/java/dotsandboxes/DotsAndBoxesGrid.java

 package dotsandboxes;
 
 
+import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Observer;
+import java.util.function.Consumer;
 
 /**
  * The state of a dots and boxes grid.
@@ -43,15 +46,60 @@ public class DotsAndBoxesGrid {
     /** Which owner (if any) claimed any given box. */
     private int[][] boxOwners;
 
-    public DotsAndBoxesGrid(int width, int height) {
+    /** A list of functions to notify when there is an update */
+    private ArrayList<Consumer<DotsAndBoxesGrid>> watchers = new ArrayList<>();
+
+    final int players;
+    private int player = 1;
+    public int getPlayer() {
+        return player;
+    }
+
+    /** Moves to the next player */
+    private void nextPlayer() {
+        player++;
+        if (player > players) {
+            player = 1;
+        }
+    }
+
+    public DotsAndBoxesGrid(int width, int height, int players) {
         this.width = width;
         this.height = height;
+        this.players = players;
 
         this.horizontals = new boolean[width - 1][height];
         this.verticals = new boolean[width][height - 1];
         this.boxOwners = new int[width - 1][height - 1];
     }
 
+    private void notifyObservers() {
+        for (Consumer<DotsAndBoxesGrid> consumer : watchers) {
+            consumer.accept(this);
+        }
+    }
+
+    /** Listens to this grid for changes */
+    public void addConsumer(Consumer<DotsAndBoxesGrid> consumer) {
+        watchers.add(consumer);
+    }
+
+    /** Returns whether a horizontal line has been drawn */
+    public boolean getHorizontal(int x, int y) {
+        return horizontals[x][y];
+    }
+
+    /** Returns whether a vertical line has been drawn */
+    public boolean getVertical(int x, int y) {
+        return verticals[x][y];
+    }
+
+    /** Returns which player owns a box. By convention, 0 is unowned. */
+    public int getBoxOwner(int x, int y) {
+        return boxOwners[x][y];
+    }
+
+
     /**
      * Checks whether a box has been fully drawn (all four sides)
      * @param x coordinate of the left side of the box
@@ -59,11 +107,8 @@ public class DotsAndBoxesGrid {
      * @return true if all four sides have been drawn.
      */
     public boolean boxComplete(int x, int y) {
-        if (x >= width - 1 || x < 0) {
-            throw new IndexOutOfBoundsException(String.format("x was %d, which is out of range. Range is 0 to %d", x, width - 1));
-        }
-        if (y >= height - 1|| y < 0) {
-            throw new IndexOutOfBoundsException(String.format("y was %d, which is out of range. Range is 0 to %d", y, height - 1));
+        if (x >= width - 1 || x < 0 || y >= height - 1 || y < 0) {
+            return false;
         }
 
         // A box is complete if the north and south horizontals and the east and west verticals have all been drawn.
@@ -71,6 +116,16 @@ public class DotsAndBoxesGrid {
         return true;
     }
 
+    /** Tries to claim a box for a player. If the box is complete, sets the ownership and returns true. */
+    private boolean claimBox(int x, int y, int p) {
+        if (boxComplete(x, y)) {
+            boxOwners[x][y] = player;
+            return true;
+        } else {
+            return false;
+        }
+    }
+
     /**
      * "Draws" a horizontal line, from grid point (x, y) to (x + 1, y). (i.e. sets that line to true)
      * @param x
@@ -88,10 +143,16 @@ public class DotsAndBoxesGrid {
         // FIXME: You need to throw an exception if the line was already drawn.
 
         this.horizontals[x][y] = true;
-        if (boxComplete(x, y)) {
-            boxOwners[x][y] = player;
+
+        // Try to claim the north or south boxes
+        boolean claimN = claimBox(x, y-1, player);
+        boolean claimS = claimBox(x, y, player);
+        if (claimN || claimS) {
+            notifyObservers();
             return true;
         } else {
+            nextPlayer();
+            notifyObservers();
             return false;
         }
     }
@@ -113,12 +174,18 @@ public class DotsAndBoxesGrid {
         // You need to throw an exception if the line was already drawn.
 
         this.verticals[x][y] = true;
-        if (boxComplete(x, y)) {
-            boxOwners[x][y] = player;
+        // Try to claim the north or south boxes
+        boolean claimE = claimBox(x, y, player);
+        boolean claimW = claimBox(x-1, y, player);
+        if (claimE || claimW) {
+            notifyObservers();
             return true;
         } else {
+            nextPlayer();
+            notifyObservers();
             return false;
         }
+
     }
 
     public boolean gameComplete() {

src/main/java/dotsandboxes/DotsAndBoxesUI.java

 package dotsandboxes;
 
+import javafx.scene.control.Label;
 import javafx.scene.layout.AnchorPane;
 import javafx.scene.paint.Color;
 import javafx.scene.shape.Circle;
 import javafx.scene.shape.Line;
+import javafx.scene.shape.Rectangle;
 
 public class DotsAndBoxesUI {
 
@@ -14,17 +16,48 @@ public class DotsAndBoxesUI {
 
     final DotsAndBoxesGrid grid;
     final AnchorPane anchorPane;
+    final Label label;
 
-    public DotsAndBoxesUI(DotsAndBoxesGrid grid) {
+    /** Colours for the different players. Only goes up to 5. */
+    final Color[] playerColours = { Color.WHITE, Color.RED, Color.BLUE, Color.GREEN, Color.PURPLE, Color.ORANGE };
+
+    private void updateLabel() {
+        label.setTextFill(playerColours[grid.getPlayer()]);
+        label.setText(String.format("Player %d's turn", grid.getPlayer()));
+    }
+
+    public DotsAndBoxesUI(final DotsAndBoxesGrid grid) {
         this.grid = grid;
         anchorPane = new AnchorPane();
 
+        label = new Label("");
+        updateLabel();
+        grid.addConsumer((g) -> updateLabel());
+
         // Size the anchorPane to just contain the elements
         int width = margin + dotDiameter + gap + (grid.width - 1) * (gap + lineLength + gap + dotDiameter) + gap + margin;
         int height = margin + dotDiameter + gap + (grid.height - 1) * (gap + lineLength + gap + dotDiameter) + gap + margin;
         anchorPane.setPrefSize(width, height);
 
 
+        // Lay out the boxes
+        for (int row = 0; row < grid.height - 1; row++) {
+            for (int col = 0; col < grid.width - 1; col++) {
+                final int x = col;
+                final int y = row;
+                Rectangle box = new Rectangle(gap, gap, lineLength, lineLength);
+                box.setFill(Color.WHITE);
+
+                grid.addConsumer((g) -> {
+                    box.setFill(playerColours[g.getBoxOwner(x, y)]);
+                });
+
+                AnchorPane.setLeftAnchor(box, gap + dotDiameter + col * (gap + lineLength + gap + dotDiameter) + dotDiameter/2.0);
+                AnchorPane.setTopAnchor(box, gap + dotDiameter + row * (gap + lineLength + gap + dotDiameter) + dotDiameter/2.0);
+                anchorPane.getChildren().add(box);
+            }
+        }
+
         // Lay out the horizontals
         for (int row = 0; row < grid.height; row++) {
             for (int col = 0; col < grid.width - 1; col++) {
@@ -32,7 +65,21 @@ public class DotsAndBoxesUI {
                 line.setStrokeWidth(dotDiameter);
                 line.setStroke(Color.DARKGREY);
 
-                line.setOnMouseClicked((evt) -> line.setStroke(Color.RED));
+                final int x = col;
+                final int y = row;
+                grid.addConsumer((g) -> {
+                    if (g.getHorizontal(x, y)) {
+                        line.setStroke(Color.BLACK);
+                    } else {
+                        line.setStroke(Color.LIGHTGRAY);
+                    }
+                });
+
+                line.setOnMouseClicked((evt) -> {try {
+                    grid.drawHorizontal(x, y, grid.getPlayer());
+                } catch (IllegalStateException ex) {
+                    // do nothing
+                }});
 
                 AnchorPane.setLeftAnchor(line, 0.0 + gap + dotDiameter + col * (gap + lineLength + gap + dotDiameter));
                 AnchorPane.setTopAnchor(line, -dotDiameter/2.0 + gap + dotDiameter + row * (gap + lineLength + gap + dotDiameter));
@@ -47,7 +94,21 @@ public class DotsAndBoxesUI {
                 line.setStrokeWidth(dotDiameter);
                 line.setStroke(Color.DARKGREY);
 
-                line.setOnMouseClicked((evt) -> line.setStroke(Color.RED));
+                final int x = col;
+                final int y = row;
+                grid.addConsumer((g) -> {
+                    if (g.getVertical(x, y)) {
+                        line.setStroke(Color.BLACK);
+                    } else {
+                        line.setStroke(Color.LIGHTGRAY);
+                    }
+                });
+
+                line.setOnMouseClicked((evt) -> {try {
+                    grid.drawVertical(x, y, grid.getPlayer());
+                } catch (IllegalStateException ex) {
+                    // do nothing
+                }});
 
                 AnchorPane.setTopAnchor(line, 0.0 + gap + dotDiameter + row * (gap + lineLength + gap + dotDiameter));
                 AnchorPane.setLeftAnchor(line, -dotDiameter/2.0 + gap + dotDiameter + col * (gap + lineLength + gap + dotDiameter));
@@ -67,8 +128,6 @@ public class DotsAndBoxesUI {
             }
         }
 
-
-
     }
 
 

src/main/java/dotsandboxes/Main.java

@@ -9,7 +9,7 @@ import javafx.stage.Stage;
 /** Our main class that launches the app. */
 public class Main extends Application {
 
-    DotsAndBoxesGrid grid = new DotsAndBoxesGrid(15, 8);
+    DotsAndBoxesGrid grid = new DotsAndBoxesGrid(15, 8, 2);
 
     @Override
     public void start(Stage primaryStage) throws Exception {
@@ -18,11 +18,12 @@ public class Main extends Application {
         Label label = new Label("My label");
 
         BorderPane borderPane = new BorderPane();
-        borderPane.setTop(label);
+        borderPane.setBottom(label);
         Scene scene = new Scene(borderPane, 600, 400);
 
         DotsAndBoxesUI dbUi = new DotsAndBoxesUI(grid);
         borderPane.setCenter(dbUi.anchorPane);
+        borderPane.setTop(dbUi.label);
 
         primaryStage.setScene(scene);