Selina Day of the year

Main.java

import java.io.IOException;
import java.util.Scanner;

public class Main {
    /**
     * @param year a year greater or equal to 1900
     * @return whether that year was a leap year
     */
    static boolean isLeapYear(int year) {
        // ...
        boolean LeapYear = false;
        if (year % 4 == 0) {
            LeapYear = true;
        }
        if (year % 100 == 0) {
            LeapYear = false;
        } 
        if (year % 400 == 0) {
            LeapYear = true;
        } 
        return LeapYear;
    }

    /**
     * @param month a month between 1 and 12
     * @param year  a year greater or equal than 1900
     * @return number of days in the month of that year
     */
    static int countDaysInMonth(int month, int year) {

        int number_Of_DaysInMonth = 0;
        boolean LeapYear = isLeapYear(year);
        switch (month) {
        case 1:
            // MonthOfName = "January";
            number_Of_DaysInMonth = 31;
            break;
        case 2:
            // MonthOfName = "February";
            if (LeapYear == true) {
                number_Of_DaysInMonth = 29;
            } else {
                number_Of_DaysInMonth = 28;
            }
            break;
        case 3:
            // MonthOfName = "March";
            number_Of_DaysInMonth = 31;
            break;
        case 4:
            // MonthOfName = "April";
            number_Of_DaysInMonth = 30;
            break;
        case 5:
            // MonthOfName = "May";
            number_Of_DaysInMonth = 31;
            break;
        case 6:
            // MonthOfName = "June";
            number_Of_DaysInMonth = 30;
            break;
        case 7:
            // MonthOfName = "July";
            number_Of_DaysInMonth = 31;
            break;
        case 8:
            // MonthOfName = "August";
            number_Of_DaysInMonth = 31;
            break;
        case 9:
            // MonthOfName = "September";
            number_Of_DaysInMonth = 30;
            break;
        case 10:
            // MonthOfName = "October";
            number_Of_DaysInMonth = 31;
            break;
        case 11:
            // MonthOfName = "November";
            number_Of_DaysInMonth = 30;
            break;
        case 12:
            // MonthOfName = "December";
            number_Of_DaysInMonth = 31;

        }
        return number_Of_DaysInMonth;
    }

    /**
     * @param day   a day between 1 and 31
     * @param month a month between 1 and 12
     * @param year  a year greater or equal than 1900
     * @return whether the date is valid
     */

    static boolean isValidDate(int day, int month, int year) {
        if (day < 1 || day > 31)
            return false;

        if (month < 1 || month > 12)
            return false;

        if (year < 1900)
            return false;

        if (day > countDaysInMonth(month, year))
            return false;

        return true;
    }

    /**
     * (the given values should represent a valid date)
     * 
     * @param day   a day between 1 and 31
     * @param month a month between 1 and 12
     * @param year  a year greater or equal than 1900
     * @return number of days between Monday January 1, 1900 and this date
     */
    static int countDays(int day, int month, int year) {
        int countTotalLeapYears = 0;
        int countDaysInFullMonth = 0;
        for (int i = 1900; i < year; i++) {
            if (isLeapYear(i) == true) {
                countTotalLeapYears += 1;
            }
        }
        for (int i = 1; i < month; i++) {
            countDaysInFullMonth += countDaysInMonth(i, year);
        }

        int TotalDays = 0;
        TotalDays = (year - 1900) * 365 + countTotalLeapYears + countDaysInFullMonth + day;
        return TotalDays;
    }

    public static void main(String[] args) throws IOException{

        Scanner input = new Scanner(System.in);
        System.out.print("Enter a day between 1 and 31 \n");
        int day = input.nextInt();
        System.out.println("Enter a month between 1 and 12\n");
        int month = input.nextInt();
        System.out.println("Enter a year greater or equal than 1900\n");
        int year = input.nextInt();

        boolean isValid = isValidDate(day, month, year);
        assert isValid : "Date not valid";

        int TotalDays = countDays(day, month, year);

        if (TotalDays % 7 == 0) {
            System.out.print("sunday");
        } else if (TotalDays % 7 == 1) {
            System.out.print("monday");
        } else if (TotalDays % 7 == 2) {
            System.out.print("tuesday");
        } else if (TotalDays % 7 == 3) {
            System.out.print("wednesday");
        } else if (TotalDays % 7 == 4) {
            System.out.print("thursday");
        } else if (TotalDays % 7 == 5) {
            System.out.print("friday");
        } else {
            System.out.print("saturday");
        }
    }
}

SelinaVersion.java

public class Main {
  /**
   * @param year   a year greater or equal to 1900
   * @return       whether that year was a leap year
   */
  static boolean isLeapYear(int year) {
    // ...
    boolean LeapYear = false;
    if (year%4 != 0 ){
      LeapYear = false;
    } else if (year%100 != 0) {
      LeapYear = true;
    } else if (year%400 != 0) {
      LeapYear = false;
    } else {
      LeapYear = true;
    }
    return LeapYear;
  }
 

  /**
   * @param month  a month between 1 and 12
   * @param year   a year greater or equal than 1900
   * @return       number of days in the month of that year
   */
  static int countDaysInMonth(int month, int year) {

    int number_Of_DaysInMonth = 0;
    boolean LeapYear = isLeapYear(year);
    switch (month) {
            case 1:
                //MonthOfName = "January";
                number_Of_DaysInMonth = 31;
                break;
            case 2:
                //MonthOfName = "February";
                if (LeapYear==true) {
                    number_Of_DaysInMonth = 29;
                } else {
                    number_Of_DaysInMonth = 28;
                }
                break;
            case 3:
                //MonthOfName = "March";
                number_Of_DaysInMonth = 31;
                break;
            case 4:
                //MonthOfName = "April";
                number_Of_DaysInMonth = 30;
                break;
            case 5:
                //MonthOfName = "May";
                number_Of_DaysInMonth = 31;
                break;
            case 6:
                //MonthOfName = "June";
                number_Of_DaysInMonth = 30;
                break;
            case 7:
                //MonthOfName = "July";
                number_Of_DaysInMonth = 31;
                break;
            case 8:
                //MonthOfName = "August";
                number_Of_DaysInMonth = 31;
                break;
            case 9:
                //MonthOfName = "September";
                number_Of_DaysInMonth = 30;
                break;
            case 10:
                //MonthOfName = "October";
                number_Of_DaysInMonth = 31;
                break;
            case 11:
                //MonthOfName = "November";
                number_Of_DaysInMonth = 30;
                break;
            case 12:
                //MonthOfName = "December";
                number_Of_DaysInMonth = 31;
  

  }
    return number_Of_DaysInMonth;
}

  /**
   * @param day    a day between 1 and 31
   * @param month  a month between 1 and 12
   * @param year   a year greater or equal than 1900
   * @return       whether the date is valid
   */
   
  static boolean isValidDate(int day, int month, int year) {
    /*assert day >= 1 && day <= 31 : "Invalid date";
    
    assert month >= 1 && month <= 12 : "Invalid date";
    
    assert year >= 1900 : "Invalid date";
    
    assert isLeapYear(year) == false && month == 2 && day > 29 : "Invalid date";
    
    return true;*/
    boolean Valid = false;
    if (isLeapYear(year)==false && month == 2 && day > 28){
      Out.print("invalid date");
      Valid = false;
    } else if (day >= 1 && day <= 31 && month >= 1 && month <= 12 && year >= 1900) {
      Out.print("invalid date");
      Valid = true;
    }
    return Valid;
    
    /*if (day >= 1 && day <= 31 && month >= 1 && month <= 12 && year >= 1900 || isLeapYear(year) == false && month == 2 && day < 29){
      return true;
    } else {
      Out.print("invalid date");
      return false;
    }*/
  }
   


  /**
   * (the given values should represent a valid date)
   * @param day    a day between 1 and 31
   * @param month  a month between 1 and 12
   * @param year   a year greater or equal than 1900
   * @return       number of days between Monday January 1, 1900 and this date
   */
  static int countDays(int day, int month, int year) {
    int countTotalLeapYears = 0;
    int countDaysInFullMonth = 0;
    for (int i = 1900; i<year; i++){
      if (isLeapYear(i)==true){
        countTotalLeapYears += 1;
      }
    }
    for (int i=1; i<month; i++){
      countDaysInFullMonth += countDaysInMonth(i, year);
    }
    
    int TotalDays = 0;
    if (year > 1901){
      TotalDays = (year - 1901) * 365 + countTotalLeapYears + countDaysInFullMonth + day;
    } else if (year == 1901){
      TotalDays = 365 + countDaysInFullMonth + day;
    } else {
      TotalDays = countDaysInFullMonth + day;
    }
    
    return TotalDays;
  }

  public static void main(String[] args) {
    
    //Out.print("Enter a day between 1 and 31");
    int day = In.readInt();
    //Out.println("Enter a month between 1 and 12");
    int month = In.readInt();
    //Out.println("Enter a year greater or equal than 1900");
    int year = In.readInt();
    
    boolean isValid = isValidDate( day, month, year );
    boolean LeapYear = isLeapYear(year);

    
    
    int TotalDays = countDays(day, month, year);
    
    if (TotalDays%7 == 0){
      Out.print("sunday");
    } else if (TotalDays%7 == 1){
      Out.print("monday");
    } else if (TotalDays%7 == 2){
      Out.print("tuesday");
    } else if (TotalDays%7 == 3){
      Out.print("wednesday");
    } else if (TotalDays%7 == 4){
      Out.print("thursday");
    } else if (TotalDays%7 == 5){
      Out.print("friday");
    } else {
      Out.print("saturday");
    }
    
    
    
   // Out.print("Enter a number: ");
  //  int n = In.readInt();
   // boolean is2019LeapYear = isLeapYear(2000);
    //Out.print(is2019LeapYear);
  }
}

Ehm ih hans halt alli Outund In miesse in System.out und System.in miesse umwandle das muesch wieder zruggwandle. Sorry