How to use if-else with String dates - if-statement

Question

I am trying to use if-else statements to get the date entered by the user and display a constant for that particular season.
So for example if I were to enter a date of 04/25/2015 I would want it to show the price for Spring. When I print the price it displays zero instead.
Any help will be great. Method will be shown below
public double determinePrice(){
double price = 0;
if(rentalDate.substring(1, 3).equals(3) || rentalDate.substring(1, 3).equals(4)|| rentalDate.substring(1, 3).equals(5))
price = SPRING;
else if(rentalDate.substring(1, 3).equals(6) || rentalDate.substring(1, 3).equals(7)|| rentalDate.substring(1, 3).equals(8))
price = SUMMER;
else if(rentalDate.substring(1, 3).equals(9) || rentalDate.substring(0, 3).equals(10)|| rentalDate.substring(0, 3).equals(11))
price = FALL;
else if(rentalDate.substring(0, 3).equals(12) || rentalDate.substring(0, 3).equals(01)|| rentalDate.substring(1, 3).equals(02))
price = WINTER;
return price;
}

Answer 1

You maybe should try to parse your string into a LocalDate and then work with these (1). With the usage of LocalDate you can define the 3 dates determining the start of summer,autumn and winter and simply check your dates like:
givenDate.isBefore(summerStartDate)
for dates in spring or
givenDate.isAfter(summerStartDate) && givenDate.isBefore(autumnStartDate)
for dates in summer...
Another possibility with the use of LocalDate would be to write a class describing timeframes with a method isIn(LocalDate) that checks whether the given date lies between start and end.
edit:
Just saw that you're only testing for the month belonging to a specific month. After parsing your original date into a LocalDate you could use the methods getMonth (gives you the month in the form of an enum value) or getMonthValue (gives you a numerical representation 1-12).
(1) Howto convert: How to parse/format dates with LocalDateTime? (Java 8)