You should create a loop that keeps prompting the user until the month is correctly inserted. Something in the following lines:
boolean correct_month = false; // Control variable
while(!correct_month)
{
int month = 0;
// Prompt the user to enter a month
SimpleIO.prompt("Enter a month name: ");
String userInput = SimpleIO.readLine();
...
// If the month is indeed correct
// then correct_month = true;
}
Then you apply the same idea to the years.
Instead of having all of those conditions on the month, I think it is better to add all the month strings into an ArrayList:
ArrayList <String> all_months = new ArrayList <String> ();
and then you just have to use all_months.indexOf
with the string insert by the user. If it returns -1 the string is not a valid month, otherwise, it will give you the position where the month is on the list. For example
month = all_months.indexOf(userInput);
if(month != -1){
correct_month = true;
}
Thus, the complete solution would be something like:
ArrayList <String> all_months = new ArrayList <String> ();
all_months.add("january");
... // and so one
int month = 0; // Control variable
while(month <= 0)
{
// Prompt the user to enter a month
SimpleIO.prompt("Enter a month name: ");
String userInput = SimpleIO.readLine();
month = all_months.indexOf(userInput.trim().toLowerCase()) + 1;
}