public static void setPlantAmount(int plantType, int amount)
	throws Exception {
	if (amount < 0) {
	    throw new Exception("The amount is not valid");
	}

	if (plantType == GREEN_PLANT) {
	    GREEN_PLANT_AMOUNT = amount;
	}
	if (plantType == RED_PLANT) {
	    RED_PLANT_AMOUNT = amount;
	}
	if (plantType == YELLOW_PLANT) {
	    YELLOW_PLANT_AMOUNT = amount;
	}
	if (plantType == MAGENTA_PLANT) {
	    MAGENTA_PLANT_AMOUNT = amount;
	}
    }