Add comments, clean up code

src/Board.java

@@ -1,32 +1,49 @@
-import java.awt.*;
+import java.awt.Color;
+import java.awt.Graphics;
 
 public class Board {
+    // Width and height of each board tile
     static final int TILE_SIZE = 64;
+    // Width and height of board in tiles
     static final int BOARD_SIZE = 8;
+    // Width and height of window in pixels
     static final int DIMENSION = TILE_SIZE * BOARD_SIZE;
     // Colors from Lost Century 24
     // https://lospec.com/palette-list/lost-century-24
+    // new Color() takes in an integer representing the color
+    // Colors are represented in hexadecimal, so we can write the hex literal by prefixing the color code with 0x
     static final Color BLACK = new Color(0x6c595c);
     static final Color WHITE = new Color(0xab9b8e);
     final DrawingPanel panel;
     final Graphics graphics;
 
+    // The board is a two-dimensional array of nullable pieces
     Piece[][] board;
+    // The current board coordinate that's being dragged
     BoardCoordinate dragging = null;
 
     public Board() {
+        // Initialize DrawingPanel
         panel = new DrawingPanel(DIMENSION, DIMENSION);
+        graphics = panel.getGraphics();
+
+        // Connect up event handlers
         panel.onMouseDown(this::handleMouseDown);
-        panel.onMouseDrag(this::draw);
+        panel.onMouseDrag((x, y) -> {
+            // We want to re-render with new mouse position when dragging pieces
+            if (dragging != null) draw(x, y);
+        });
         panel.onMouseUp(this::handleMouseUp);
-        graphics = panel.getGraphics();
+
+        // Initialize board
         board = new Piece[BOARD_SIZE][BOARD_SIZE];
-        for (int y = 0; y < 2; y++) {
+
+        // Initialize pieces
+        for (int y = 0; y < 2; y++)
             for (int x = 0; x < BOARD_SIZE; x++) {
                 set(x, y, new Piece(true));
                 set(x, y + 6, new Piece(false));
             }
-        }
     }
 
     public Piece get(int x, int y) {
@@ -54,30 +71,46 @@ public class Board {
         move(from.x, from.y, to.x, to.y);
     }
 
+    // Mouse down event handler
+    // This sets the currently dragging piece
     void handleMouseDown(int x, int y) {
+        // Get board coordinate of mouse click
         BoardCoordinate coordinate = new ScreenCoordinate(x, y).toBoard();
+        // If there's no piece there, return
         if (get(coordinate) == null) return;
+        // Set currently dragging piece to that coordinate
         dragging = coordinate;
+        // Redraw with dragging
         draw(x, y);
     }
 
     void handleMouseUp(int x, int y) {
+        // Get board coordinate of mouse release
         BoardCoordinate newCoordinate = new ScreenCoordinate(x, y).toBoard();
+        // Only do something if new coordinate is different from the originating coordinate
         if (!dragging.equals(newCoordinate)) {
+            // Get piece on target coordinate
             Piece capturedPiece = get(newCoordinate);
+            // Only move piece to square if there's nothing there, or they are of differing colors
             if (capturedPiece == null || capturedPiece.black != get(dragging).black) {
                 move(dragging, newCoordinate);
             }
         }
+        // Clear dragging
         dragging = null;
+        // Redraw without dragging
         draw();
     }
 
     public void draw() {
-        draw(0, 0);
+        draw(null);
     }
 
     public void draw(int mouseX, int mouseY) {
+        draw(new ScreenCoordinate(mouseX, mouseY));
+    }
+
+    public void draw(ScreenCoordinate mousePosition) {
         // Draw board
         graphics.setColor(WHITE);
         graphics.fillRect(0, 0, DIMENSION, DIMENSION);
@@ -85,21 +118,18 @@ public class Board {
         for (int y = 0; y < BOARD_SIZE; y++)
             for (int x = y % 2; x < BOARD_SIZE; x += 2)
                 graphics.fillRect(x * TILE_SIZE, y * TILE_SIZE, TILE_SIZE, TILE_SIZE);
-        // Draw pieces
 
-        forEachPiece((coordinate, piece) -> {
-            int x, y;
-            if (coordinate.equals(dragging)) {
-                x = mouseX;
-                y = mouseY;
-            } else {
-                x = coordinate.x * TILE_SIZE + TILE_SIZE / 2;
-                y = coordinate.y * TILE_SIZE + TILE_SIZE / 2;
-            }
-            piece.draw(graphics, x, y);
+        // Draw pieces
+        forEachPiece((boardCoordinate, piece) -> {
+            // If piece is the one being dragged, render it at the mouse position
+            // Otherwise, render it at the center of the board tile
+            piece.draw(graphics, boardCoordinate.equals(dragging) ? mousePosition : boardCoordinate.toScreen());
         });
     }
 
+    // Functional interfaces for forEachPiece
+    // Provide ability to run code for each piece on board without having to duplicate nested for loop boilerplate
+
     @FunctionalInterface
     interface PieceActionXY {
         void forEachTile(int x, int y, Piece piece);
@@ -110,17 +140,26 @@ public class Board {
         void forEachTile(BoardCoordinate coordinate, Piece piece);
     }
 
+    // Run code on each tile on board
+    // Usage:
+    // forEachPiece((x, y, piece) -> {
+    //     // do something with piece
+    // });
     public void forEachPiece(PieceActionXY tileAction) {
         for (int y = 0; y < BOARD_SIZE; y++)
             for (int x = 0; x < BOARD_SIZE; x++) {
-                Piece piece = board[y][x];
+                Piece piece = get(x, y);
                 if (piece == null) continue;
                 tileAction.forEachTile(x, y, piece);
             }
     }
 
+    // Run code on each tile on board
+    // Usage:
+    // forEachPiece((coordinate, piece) -> {
+    //     // do something with piece
+    // });
     public void forEachPiece(PieceActionCoordinate tileAction) {
-        forEachPiece((x, y, piece) -> tileAction.forEachTile(new BoardCoordinate(x, y), board[y][x]));
+        forEachPiece((x, y, piece) -> tileAction.forEachTile(new BoardCoordinate(x, y), get(x, y)));
     }
-}
-
+}

src/BoardCoordinate.java

@@ -1,12 +1,23 @@
+// Board coordinate class.
+// Provides tile coordinates for squares on the chess board.
 public class BoardCoordinate extends Coordinate {
     public BoardCoordinate(int x, int y) {
-        super(x, y);
+        super(x, y); // Execute superclass constructor
+    }
+
+    // TODO: reimplement as casting
+    // Convert to screen coordinate by getting center pixel of tile
+    public ScreenCoordinate toScreen() {
+        return new ScreenCoordinate(
+                x * Board.TILE_SIZE + Board.TILE_SIZE / 2,
+                y * Board.TILE_SIZE + Board.TILE_SIZE / 2
+        );
     }
 
     @Override
     public boolean equals(Object obj) {
-        if (obj == this) return true;
-        if (!(obj instanceof BoardCoordinate other)) return false;
-        return other.x == x && other.y == y;
+        if (obj == this) return true; // Equals if same object
+        if (!(obj instanceof BoardCoordinate other)) return false; // If other is not BoardCoordinate, not equals
+        return other.x == x && other.y == y; // If is BoardCoordinate and x- and y-values match, equals
     }
 }

src/Coordinate.java

@@ -1,5 +1,5 @@
-import java.util.Objects;
-
+// Generic abstract Coordinate class for storing an (x, y) pair.
+// BoardCoordinate and ScreenCoordinate inherit from this.
 public abstract class Coordinate {
     public int x;
     public int y;

src/Piece.java

@@ -1,17 +1,28 @@
 import java.awt.*;
 
 public class Piece {
+    // Width and height of placeholder rectangle graphic
     public static final int DIMENSION = 32;
     public boolean black;
 
+    // If no parameter, default to white
     public Piece() { }
 
     public Piece(boolean black) {
         this.black = black;
     }
 
+    // The Piece class doesn't store position,
+    // so when drawing we need to be provided this along with a graphics context when drawing
     public void draw(Graphics graphics, int x, int y) {
         graphics.setColor(black ? Color.BLACK : Color.WHITE);
+        // Drawing is performed from the top-left corner.
+        // We need the drawn rectangle to be offset by half of the width and height
+        // so it is centered on the provided position.
         graphics.fillRect(x - DIMENSION / 2, y - DIMENSION / 2, DIMENSION, DIMENSION);
     }
+
+    public void draw(Graphics graphics, ScreenCoordinate coordinate) {
+        draw(graphics, coordinate.x, coordinate.y);
+    }
 }

src/ScreenCoordinate.java

@@ -1,17 +1,21 @@
+// Screen coordinate class.
+// Holds pixel coordinates relative to window.
 public class ScreenCoordinate extends Coordinate {
     public ScreenCoordinate(int x, int y) {
-        super(x, y);
+        super(x, y); // Execute superclass constructor
     }
 
+    // TODO: reimplement as casting
     public BoardCoordinate toBoard() {
+        // We can convert to board coordinates by dividing by the tile size of each square on the board
         return new BoardCoordinate(x / Board.TILE_SIZE, y / Board.TILE_SIZE);
     }
 
     @Override
     public boolean equals(Object obj) {
-        if (obj == this) return true;
-        if (obj instanceof BoardCoordinate) return obj == toBoard();
-        if (!(obj instanceof ScreenCoordinate other)) return false;
-        return other.x == x && other.y == y;
+        if (obj == this) return true; // Equals if same object
+        if (obj instanceof BoardCoordinate) return obj == toBoard(); // If other is BoardCoordinate, we can see if they match
+        if (!(obj instanceof ScreenCoordinate other)) return false; // If not BoardCoordinate or ScreenCoordinate, not equals
+        return other.x == x && other.y == y; // If is ScreenCoordinate and x- and y-values match, equals
     }
 }