i put getValidMove into move class for more clarity

src/backend/Board.java

@@ -14,6 +14,7 @@ public class Board {
     private boolean turnWhite = true;
     private ArrayList<int[]> highlightedSquares = new ArrayList<>();
     private int[] enPassantTarget = null; // [x,y] coordinates of en passant target square
+    private Move moveHelper = new Move();
     
     public Board(int colNum, int lineNum) {
         this.width = colNum;
@@ -192,7 +193,7 @@ public class Board {
                 selectedX = x;
                 selectedY = y;
                 hasSelectedPiece = true;
-                highlightedSquares = getValidMoves(clicked);
+                highlightedSquares = moveHelper.getValidMoves(clicked, board, width, height, enPassantTarget);
             }
         } else {
             // Check if clicked again on the same square to unselect

src/backend/Move.java

@@ -1,5 +1,55 @@
 package backend;
 
+import java.util.ArrayList;
+
 public class Move {
-	
+    
-}
+
+    public ArrayList<int[]> getValidMoves(Piece piece, Piece[][] board, int width, int height, int[] enPassantTarget) {
+        ArrayList<int[]> moves = new ArrayList<>();
+        int x = piece.getX();
+        int y = piece.getY();
+        PieceType type = piece.getType();
+
+        if (type == PieceType.Pawn) {
+            int dir = piece.isWhite() ? 1 : -1;
+            int startRow = piece.isWhite() ? 1 : 6;
+
+            int oneStep = y + dir;
+            if (inBounds(x, oneStep, width, height) && board[x][oneStep] == null) {
+                moves.add(new int[]{x, oneStep});
+                int twoStep = y + 2 * dir;
+                if (y == startRow && inBounds(x, twoStep, width, height) &&
+                    board[x][twoStep] == null && board[x][oneStep] == null) {
+                    moves.add(new int[]{x, twoStep});
+                }
+            }
+
+            for (int dx : new int[]{-1, 1}) {
+                int nx = x + dx;
+                int ny = y + dir;
+                if (inBounds(nx, ny, width, height)) {
+                    if (board[nx][ny] != null && board[nx][ny].isWhite() != piece.isWhite()) {
+                        moves.add(new int[]{nx, ny});
+                    }
+                    else if (board[nx][ny] == null && enPassantTarget != null &&
+                             nx == enPassantTarget[0] && ny == enPassantTarget[1]) {
+                        int capturedY = y;
+                        if (inBounds(nx, capturedY, width, height) &&
+                            board[nx][capturedY] != null &&
+                            board[nx][capturedY].getType() == PieceType.Pawn &&
+                            board[nx][capturedY].isWhite() != piece.isWhite()) {
+                            moves.add(new int[]{nx, ny});
+                        }
+                    }
+                }
+            }
+        }
+
+        return moves;
+    }
+
+    private boolean inBounds(int x, int y, int width, int height) {
+        return x >= 0 && x < width && y >= 0 && y < height;
+    }
+}