這個問題的第一步是switch語句.最好不要在另外一個對象的基礎上使用switch. 如果不得不使用,也應該在對象自己的數據上使用,而不是在別人數據上使用 Rental類 ~~~ public double getCharge(double thisAmount) { switch (getMovie().getPriceCode()) { case Movice.REGULAR: thisAmount += 2; if (getDaysRented() > 2) thisAmount += (getDaysRented() - 2) * 1.5; break; case Movice.NEW_RELEASE: thisAmount += getDaysRented() * 3; break; case Movice.CHILDRENS: thisAmount += 1.5; if (getDaysRented() > 3) thisAmount += (getDaysRented() - 3) * 1.5; break; } return thisAmount; } ~~~ 這暗示getCharge應該寫到Movie類里面 Movice類 ~~~ public double getCharge(double thisAmount, Rental rental) { switch (rental.getMovie().getPriceCode()) { case REGULAR: thisAmount += 2; if (rental.getDaysRented() > 2) thisAmount += (rental.getDaysRented() - 2) * 1.5; break; case NEW_RELEASE: thisAmount += rental.getDaysRented() * 3; break; case CHILDRENS: thisAmount += 1.5; if (rental.getDaysRented() > 3) thisAmount += (rental.getDaysRented() - 3) * 1.5; break; } return thisAmount; } ~~~