GetWeekDayName.java

package com.javamultiplex.datetime;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Scanner;

/**
 * 
 * @author Rohit Agarwal
 * @category Date and Time
 * @problem How to get day name of given date?
 *
 */
public class GetWeekDayName {

	public static void main(String[] args) {

		Scanner input=null;
		try
		{
			input=new Scanner(System.in);
			System.out.println("Enter date in dd/MM/yyyy format :");
			String date=input.next();
			//If Date is valid, converting String to Date
			Date mydate=getValidDate(date);
			if(mydate!=null)
			{
				//Creating Calendar class instance.
				Calendar calendar=Calendar.getInstance();
				//Converting Date to Calendar.
				calendar.setTime(mydate);
			    int dayofWeek=calendar.get(Calendar.DAY_OF_WEEK);
				String dayName=getDayName(dayofWeek);
				System.out.println("Day : "+dayName);
			}
			else
			{
				System.out.println("Date is invalid.");
			}
		}
		finally
		{
			if(input!=null)
			{
				input.close();
			}
		}
	
		
	}
	
private static Date getValidDate(String date) {
		
		Date mydate=null;
		if(isValidDateFormat(date))
		{
			/*
			 * d -> Day of month
			 * M -> Month of year
			 * y -> Year
			 */
			DateFormat dateFormat=new SimpleDateFormat("dd/MM/yyyy");
			/*
			 * By default setLenient() is true.
			 * We should make it false for strict date validations.
			 * 
			 * If setLenient() is true - It accepts all dates.
			 * If setLenient() is false - It accepts only valid dates.
			 */
			dateFormat.setLenient(false);
			try {
				mydate=dateFormat.parse(date);
			} catch (ParseException e) {
				mydate=null;
			}
		}
		return mydate;
	}

private static String getDayName(int dayofWeek) {
		
		String dayName=null;
		switch(dayofWeek)
		{
		case 1:
			dayName="Sunday";
			break;
		case 2:
			dayName="Monday";
			break;
		case 3:
			dayName="Tuesday";
			break;
		case 4:
			dayName="Wednesday";
			break;
		case 5:
			dayName="Thursday";
			break;
		case 6:
			dayName="Friday";
			break;
		case 7:
			dayName="Saturday";
			break;
		}
		return dayName;
	}

	
	private static boolean isValidDateFormat(String date) {
		
		/*
		 * Regular Expression that matches String with format dd/MM/yyyy.
		 * dd -> 01-31
		 * MM -> 01-12
		 * yyyy -> 4 digit number
		 */
		String pattern="(0?[1-9]|[12][0-9]|3[01])\\/(0?[1-9]|1[0-2])\\/([0-9]{4})";
		boolean result=false;
		if(date.matches(pattern))
		{
			result=true;
		}
		return result;
	}
	
}