Shaz Software Solutions

This program runs in Windows 7 Command Line

Find the day of the week of a given date using Java language

Class: DayWeek.java
Author: Shahrzad Jahangirian
Language: Java (using Java 7)
Date Added: Dec 20, 2016
Description: After publishing many large Java Database Application in my Website, this time for end of 2016 I developed a small Java Program to Find the day of the week of a given date. I find this problem at http://www.home.hs-karlsruhe.de/~pach0003/informatik_1/aufgaben/en/flowcontrol.html#day_of_week. There is a solution for this problem in that page, but I designed and developed my own solution as you see below before I looked at their solution for the problem.
This is the problem description exactly as you find in above web page:

Find the day of the week of a given date

degree of difficulty: 2
Implement a Java-method that prints out the day of the week for a given day (1..31), month (1..12) and year.
The day of the week of dates between March 1900 and February 2100 can be calculated as follows:
First, you have to calculate the total number of days from 1900/1/1 to the given date (see below, for details). Secondly, you divide this number by 7 with integer remainder: this now is the day of the week, with 0 as sunday, 1 as monday, etc. To calculate the total number of days you have to implement the following steps:
Subtract 1900 from the given year and multiply the result by 365
Add the missing leaps years by adding (year - 1900) / 4.
If the year itself is a leap year and the month is January or February, you have to subtract 1 from the previous result.
Now add the all days of the year up to the given one to the result (in case of february always 28, because the additional day for a leap year already have been added).
Here some dates with the day of the week for testing your Java programm:
Easter Sunday: 1916/3/23, 2007/4/8, 2010/4/4
Ash Wednesday: 2006/3/1, 2007/2/21, 2010/2/17

How to Run: I run this program in Windows 7 Command line Prompt with Java(TM) SE Runtime Environment 7 on my computer as you see above
Compile and Run it as below:
C:\javacodes> javac DayWeek.java "compiles the DayWeek class"
C:\javacodes> Java DayWeek "and to run it"

Class: DayWeek.java

/*
 Class: DayWeek
 Author: Shahrzad Jahangirian
 Date: December 2016
 Description: This is a Java Program with main and all other methods in one file.
 The objective of this class is to "Find the day of the week of a given date" that
 entered by user through command line.
 */

import java.util.*;
import java.text.*;
import java.io.*;

public class DayWeek {

private int leapArr[] = {
      1900, 1904, 1908, 1912, 1916, 1920, 1924, 1928, 1932, 1936, 1940, 1944,
      1948, 1952, 1956, 1960, 1964, 1968, 1972, 1976, 1980, 1984, 1988, 1992,
      1996, 2000, 2004, 2008, 2012, 2016, 2020, 2024, 2028, 2032, 2036, 2040,
      2044, 2048, 2052, 2056, 2060, 2064, 2068, 2072, 2076, 2080, 2084, 2088,
      2092, 2096, 2100};
  private int monthDaysArr[] = {
      31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
  private int userYear = 0;
  private int userMonth = 0;
  private int userDay = 0;
  private int userMonthDays = 0;
  private String str = new String();
  private SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd");
  private InputStreamReader isr = new InputStreamReader(System.in);
  private BufferedReader br = new BufferedReader(isr);

public static void main(String[] args) {
    DayWeek dw = new DayWeek();
    try {
      dw.calculateDayOfTheWeek();
    }
    catch (Exception ex) {
      System.out.println(ex.getMessage());
    }
  }

public void getUserInput() {
    boolean valid = false;
    try {
      do {
        System.out.println("Enter a Date to get its Day Of The Week");
        System.out.print("In range of Mar 1900 to Feb 2100 (eg: 2016/12/14): ");
        str = new String();
        str = br.readLine();
        valid = validateInput(str);
      }
      while (valid == false);
    }
    catch (Exception ex) {
      System.out.println(ex.getMessage());
    }
  }

public boolean validateInput(String str) {
    try {
      sdf.parse(str);
      return true;
    }
    catch (Exception ex) {
      return false;
    }
  }

public void calculateDayOfTheWeek() throws Exception {
    int daysTotal = 0;
    int weekDay;
    String weekDayStr = new String();
    boolean flag = true;

getUserInput();
    while (flag == true) {
      try {
        StringTokenizer st = new StringTokenizer(str, "/");
        userYear = Integer.parseInt(st.nextToken());
        userMonth = Integer.parseInt(st.nextToken());
        userDay = Integer.parseInt(st.nextToken());
        daysTotal = (userYear - 1900) * 365;
        daysTotal = daysTotal + ( (userYear - 1900) / 4);
        if ( (isLeapYear() == true) && (isJanFeb() == true)) {
          daysTotal = daysTotal - 1;
        }
        int temp = userMonth - 1;
        for (int j = 0; j < temp; j++) {
          userMonthDays = userMonthDays + monthDaysArr[j];
        }
        userMonthDays = userMonthDays + userDay;
        daysTotal = daysTotal + userMonthDays;
        weekDay = daysTotal % 7;
        switch (weekDay) {
          case 0:
            weekDayStr = "Sunday";
            break;
          case 1:
            weekDayStr = "Monday";
            break;
          case 2:
            weekDayStr = "Tuesday";
            break;
          case 3:
            weekDayStr = "Wednesday";
            break;
          case 4:
            weekDayStr = "Thursday";
            break;
          case 5:
            weekDayStr = "Friday";
            break;
          case 6:
            weekDayStr = "Saturday";
            break;
        }
        System.out.println(weekDayStr + " is the Day of the Week for " + str + "\n\n");
        userMonthDays = 0;
        weekDay = 0;
      }
      catch (Exception ex) {
        System.out.println(ex.getMessage());
      }
      System.out.print("Type Q to Quit or press any key to continue . .  . ");
      str = new String();
      str = br.readLine();
      if (str.equalsIgnoreCase("Q") == true) {
        System.exit(0);
      }
      else {
        getUserInput();
      }
    }
  }

public boolean isLeapYear() {
    boolean leap = false;
    for (int i = 0; i < leapArr.length; i++) {
      if (leapArr[i] == userYear) {
        leap = true;
      }
    }
    return leap;
  }

public boolean isJanFeb() {
    boolean janFeb = false;
    if ( (userMonth == 1) || (userMonth == 2)) {
      janFeb = true;
    }
    return janFeb;
  }

}