save / load partially fixed, still an error with cells and selectedcell

src/backend/Board.java

@@ -173,10 +173,50 @@ public class Board {
 	}
 
 	public String[] toFileRep() {
-		return null;
+		ArrayList<String> lines = new ArrayList<>();
+	    for (int y = 0; y < 8; y++) {
+	        for (int x = 0; x < 8; x++) {
+	            Piece piece = cells[x][y];
+	            if (piece != null) {
+	                String line = piece.getType() + " " + piece.isWhite() + " " + x + " " + y;
+	                lines.add(line);
+	            }
+	        }
+	    }
+
+	    return lines.toArray(new String[0]);
 	}
 
+	//loading feature
 	public Board(String[] array) {
+		this.cNum = 8;
+	    this.lNum = 8;
+	    this.cells = new Piece[cNum][lNum];
+	    this.selectedCell = null;
+
+	    //clean board
+	    for (int y = 0; y < 8; y++) {
+	        for (int x = 0; x < 8; x++) {
+	            cells[x][y] = null;
+	        }
+	    }
+
+	    //load pieces
+	    for (String line : array) {
+	        String[] tokens = line.trim().split("\\s+");
+	        if (tokens.length != 4) continue;
+
+	        try {
+	            PieceType type = PieceType.valueOf(tokens[0]);
+	            boolean isWhite = Boolean.parseBoolean(tokens[1]);
+	            int x = Integer.parseInt(tokens[2]);
+	            int y = Integer.parseInt(tokens[3]);
+
+	            setPiece(isWhite, type, x, y);
+	        } catch (Exception e) {
+	            System.err.println("Error parsing line: " + line);
+	        }
+	    }
 	}
 
 	public boolean isHighlighted(int destX, int destY) {