checking boudaries

app/src/main/java/sudoku/Sudoku.java

@@ -21,11 +21,21 @@ public class Sudoku {
 		this.constraints = constraints;
 	}
 
+	/**
+	 * @return wether the coords are in the sudoku
+	 */
+	public boolean isValidCoords(int x, int y) {
+		int index = y * getSize() + x;
+		return index < getSize() * getSize();
+	}
+
 	/**
 	 * Try to place a cell at the given coordinate
+	 * 
 	 * @return false if it can't be done
 	 */
 	public boolean setCellSymbol(int x, int y, int value) {
+		assert (isValidCoords(x, y));
 		for (IConstraint constraint : this.constraints) {
 			if (!constraint.canBePlaced(this, x, y, value)) {
 				return false;
@@ -41,7 +51,7 @@ public class Sudoku {
 
 	public Cell getCell(int x, int y) {
 		int index = y * getSize() + x;
-		assert(index < getSize() * getSize());
+		assert (isValidCoords(x, y));
 		return this.cells.get(index);
 	}
 
@@ -100,8 +110,7 @@ public class Sudoku {
 			if (x == size - 1) {
 				y += 1;
 				x = 0;
-			}
-			else {
+			} else {
 				x += 1;
 			}
 		}