Diagnosis System Program: walk thru

public class DiagnosisSystem {
public static final int JANUARY = 1;
public static final int FEBRUARY = 2;
public static final int NOVEMBER = 11;
public static final int DECEMBER = 12;
public static final int DAYS_PER_YEAR = 365;
public static final int[] DAYS_PER_MONTH = {0,
// 1, 2 , 3 , 4, 5 , 6, 7 , 8 , 9 , 10, 11, 12
 31, 28, 31, 30, 31, 30, 31, 31, 30, 30, 30, 31,
 };
/**
 *Runs programs to return patient's results
 *@param args command line argument
 *@returns reults of test
 */
 public static void main(String [] args) {
    Scanner console = new Scanner(System.in);
    System.out.println("       Welcome to the Diagnosis Decision Support System");
    System.out.println("When prompted, please enter today's month and day (e.g., 3 14),");
    System.out.println("the patient's full name, temperature, and whether the patient");
    System.out.println("is experiencing congestion, aches, and/or a rash. A diagnosis");
    System.out.println("of Healthy, Cold, Flu, Measles, or Uncertain will be output as");
    System.out.println("well as a return date, if the diagnosis is Measles or Uncertain.");
    String patient;
    int month = 0;
    int day = 0;
    double temperature = 0;
    String congestion;
    String aches;
    String rash;
    System.out.println("Patient: ");
    patient = console.nextLine();
    System.out.println("Month Day (e.g., 3 14): ");
    month = console.nextInt();
    day = console.nextInt();
    System.out.println("Temperature: ");
    temperature = console.nextDouble();
    System.out.println("Congestion (y,n): ");
    congestion = console.next();
    boolean c = false;
    if (congestion.equals("y")) {
    c = true;
    }
    System.out.println("Aches (y,n): ");
    aches = console.next();
    boolean a = false;
    if (aches.equals("y")) {
    a =  true;
    }
    System.out.println("Rash (y,n): ");
    rash = console.next();
    boolean r = false;
    if (rash.equals("y")) {
    r = true;
    }
    String d = getDiagnosis(temperature, c , a, r);
    System.out.println("Patient: " + patient);
    System.out.println("Temperature: " + temperature);
    System.out.println("Diagnosis: " + d);
    isValidDate(month, day);
    if (isValidDate(month, day)) {
    String b = getReturnDate(month, day);
    System.out.println("Return date: " + b );
    } else {
    System.out.println("Return date: ");
    }
}

        /**
         *Validates the date entered 
         *@param month int
         *@param day int
         *@return true if valid month or day, false if invalid month or day
         */
     //Return true if the date is a valid date during 2015
   //Return false otherwise 
        public static boolean isValidDate( int month, int day) {
            boolean validDate;
            if ((month >= 1 ||  month <= 12) && (day >= 1 || day <= 31)) {
            validDate = true;
            }
            if ((month == 4 || month == 6 || month == 9 || month == 11) && (day <= 30)) {
            validDate = true;
            }
            if((month == 1 || month == 2 || month ==3 || month ==5 || month == 7 || month == 8 || month == 10 || month == 12) && (day <= 31)) {
            validDate = true;
            }
            if ((month == 2) && (day < 28)) {
            validDate = true;
            } else {
            return false;   
            }return false;
        } 
            /**
             *
             *
             */
     //Determine and return the diagnosis (Healthy, Cold, Flu, Measles, Uncertain)
    //based on a patient's symptoms and the chart given above.
            public static String getDiagnosis(double temperature, boolean congestion, boolean aches, boolean rash) {
                if (temperature < 99) {
                    if(!congestion && !aches && !rash)
                        System.out.println("Healthy");
                } else if (temperature < 100) {
                    if (congestion && !aches && !rash)
                        System.out.println("Cold");
                }
                if (temperature >= 100) {
                    if(!congestion && aches && !rash)
                        System.out.println("Flu");
                }
                if ( temperature >= 100) {
                    if(!congestion && !aches && rash) 
                        System.out.println("Measles");
                } else {
                        System.out.println("Uncertain");
                } return "Uncertain";
            }          
                /**
                 *Throw an IllegalArgumentException if the month and day is not a valid
                 *date in 2015
                 *Return a date formatted as month/day/year, e.g., 12/9/2015, that occurs
                 *3 days after the given month and day in 2015
                 *@param month int months in 2015
                 *@param day int days in 2015
                 *@param year int year of 2015
                 */
                public static String getReturnDate(int month, int day) throws IllegalArgumentException {
                    int year = 2015;
                    String s4 = (month + "/" + day + "/" + year);
                    if ((month < 1 ||  month > 12) && (day < 1 || day > 31)) {
                        throw new IllegalArgumentException("Invalid response");
                    }
                    int days[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
                    day = day + 3;
                    if (day > days[month]) {
                        month++;
                    }
                    if (day > days[year]) {
                        year++;
                    } return s4;
                } 

}