Day of the week GUI

/** @author Georgi Christov ( a.k.a. 8masterofpuppets8 )
 *  @version 1.0
 *  @since 12.10.2009 */

import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

class DayOfWeek {
	
	private String day;
	private String month;
	private String year;
	
	public DayOfWeek( String d, String m, String y ) {
		day = d; month = m; year = y;
	}
	
	private int changeMonth( String m ) {
		if ( month.equalsIgnoreCase( "January" ) )
			return 1;
		else if ( month.equalsIgnoreCase( "February" ) )
			return 2;
		else if ( month.equalsIgnoreCase( "March" ) )
			return 3;
		else if ( month.equalsIgnoreCase( "April" ) )
			return 4;
		else if ( month.equalsIgnoreCase( "May" ) )
			return 5;
		else if ( month.equalsIgnoreCase( "June" ) )
			return 6;
		else if ( month.equalsIgnoreCase( "July" ) )
			return 7;
		else if ( month.equalsIgnoreCase( "August" ) )
			return 8;
		else if ( month.equalsIgnoreCase( "September" ) )
			return 9;
		else if ( month.equalsIgnoreCase( "October" ) )
			return 10;
		else if ( month.equalsIgnoreCase( "November" ) )
			return 11;
		else if ( month.equalsIgnoreCase( "December" ) )
			return 12;
		return Integer.parseInt( month );
	}
	
	public boolean isLeap( int y ) {
		if ( y % 4 == 0 && y % 100 != 0 ) {
			return true;
		}
		else if ( y % 4 == 0 && y % 100 == 0 ) {
			if ( y % 400 == 0 ) return true;
		}
		return false;
	}
	
	private String calculateDayOfWeek( int day, int month, int year ) {
		// Considering the fact that 01.01.1900 fell on a Monday
		int startYear = 1900, startDay = 0, daysInCurrentMonth = 0;
		int yearCounter = startYear, daysOfYear;
		int totalDays = 0;
		boolean leapYear = false;
		String finalDay = "";
		
		/* This first loop is used to calculate the years from 1900 up to but excluding the
		   input year */
		while ( yearCounter <= year ) {
			leapYear = false;
			daysOfYear = 365;
			
			// Check if the current year is a leap-year or not
			if ( yearCounter % 4 == 0 && yearCounter % 100 != 0 ) {
				leapYear = true;
			}
			else if ( yearCounter % 4 == 0 && yearCounter % 100 == 0 ) {
				if ( yearCounter % 400 == 0 ) leapYear = true;
			}
			if ( leapYear ) daysOfYear = 366;
			
			// This check is used because we don't need all days from the last year
			if ( yearCounter < year ) totalDays += daysOfYear;
			yearCounter += 1;
		}
		
		/* Here the program has reached the input year and need to add the missing
		   month values */
		for ( int count = 1; count < month; count++ ) {
			switch ( count ) {
				case 1: daysInCurrentMonth = 31; break;
				case 2: {
					if ( leapYear ) daysInCurrentMonth = 29;
					else daysInCurrentMonth = 28; 
					break;
				}
				case 3: daysInCurrentMonth = 31; break;
				case 4: daysInCurrentMonth = 30; break;
				case 5: daysInCurrentMonth = 31; break;
				case 6: daysInCurrentMonth = 30; break;
				case 7: daysInCurrentMonth = 31; break;
				case 8: daysInCurrentMonth = 31; break;
				case 9: daysInCurrentMonth = 30; break;
				case 10: daysInCurrentMonth = 31; break;
				case 11: daysInCurrentMonth = 30; break;
				case 12: daysInCurrentMonth = 31; break;
			}
			totalDays += daysInCurrentMonth;
		}
		
		totalDays += day; // Add remaining days to the ones calculated so far
		// Find the day of the week having in mind that 1.1.1900 fell on a Monday
		if ( totalDays > 7 ) {
			if ( totalDays % 7 != 0 ) startDay = totalDays % 7; // Where the remainder is the day needed
			else startDay = 7; // In this case the day is always Sunday
		}
		else startDay = day;
			
		if ( startDay == 1 ) finalDay = "Monday";
		else if ( startDay == 2 ) finalDay = "Tuesday";
		else if ( startDay == 3 ) finalDay = "Wednesday";
		else if ( startDay == 4 ) finalDay = "Thursday";
		else if ( startDay == 5 ) finalDay = "Friday";
		else if ( startDay == 6 ) finalDay = "Saturday";
		else if ( startDay == 7 ) finalDay = "Sunday";
		
		return finalDay;
	}
	public String calculateDay() {
		return calculateDayOfWeek( Integer.parseInt( day ), changeMonth( month ), Integer.parseInt( year ) );
	}
}
	
public class ApplicationDemo extends JPanel implements ActionListener {
	private static final long serialVersionUID = 1L;
	
	JTextField resultField, yearField;
	JFrame frame;
	JPanel panel;
	JButton calculateButton, exitButton, resetButton;
	JLabel dLabel, mLabel, yLabel;
	JComboBox dayValues, monthValues;
	String d = "1", m = "January";
	
	@SuppressWarnings( "deprecation" )
	public ApplicationDemo() {
		frame = new JFrame( "DayOfWeek" );
		panel = new JPanel();
		panel.setLayout( null );
		
		String days[] = { "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20",
				          "21", "22", "23", "24", "25", "26", "27", "28", "29", "30", "31" };
		String months[] = { "January", "February", "March", "April", "May", "June", "July",
				          "August", "September", "October", "November", "December" };
		
		dayValues = new JComboBox( days ); dayValues.setBounds( 20, 25, 50, 24 );
		dayValues.addActionListener( this ); dayValues.setBackground( Color.WHITE );
		monthValues = new JComboBox( months ); monthValues.setBounds( 95, 25, 100, 24 );
		monthValues.addActionListener( this ); monthValues.setBackground( Color.WHITE );
		yearField = new JTextField(); yearField.setHorizontalAlignment( JTextField.CENTER );
		yearField.setBounds( 220, 25, 50, 25 );
		yearField.setToolTipText( "Enter year >= 1900." );
		
		dLabel = new JLabel(); dLabel.setText( "Day" ); dLabel.setBounds( 33, 3, 30, 25 );
		mLabel = new JLabel(); mLabel.setText( "Month" ); mLabel.setBounds( 125, 3, 35, 25 );
		yLabel = new JLabel(); yLabel.setText( "Year" ); yLabel.setBounds( 230, 3, 33, 25 );
		
		calculateButton = new JButton( "Calculate day of week" );
		calculateButton.addActionListener( this );
		exitButton = new JButton( "Exit" );
		exitButton.addActionListener( this );
		resetButton = new JButton( "Reset" );
		resetButton.addActionListener( this );
		
		exitButton.setBounds( 150, 130, 80, 25 );
		calculateButton.setBounds( 65, 60, 160, 25 );
		resetButton.setBounds( 60, 130, 80, 25 );
		calculateButton.setToolTipText( "Calculate day of the week." );
		exitButton.setToolTipText( "Close program." );
		resetButton.setToolTipText( "Reset all fields." );
		
		resultField = new JTextField();
		resultField.setHorizontalAlignment( JTextField.CENTER );
		resultField.setBounds( 45, 95, 200, 25 );
		resultField.setEditable( false );
		
		panel.add( yearField ); panel.add( dayValues ); panel.add( monthValues );
		panel.add( calculateButton ); panel.add( resultField );
		panel.add( exitButton ); panel.add( resetButton );
		panel.add( dLabel ); panel.add( mLabel ); panel.add( yLabel );
		
		frame.setContentPane( panel );
		frame.setBounds( 470, 200, 300, 200 );
		frame.setDefaultCloseOperation( 0 );
		frame.show();
	}

	public void actionPerformed( ActionEvent e ) {
		if ( e.getSource() == calculateButton ) {
			DayOfWeek classObject = new DayOfWeek( d, m, yearField.getText() );
			String result = "";
			try {
				if ( !classObject.isLeap( Integer.parseInt( yearField.getText() ) ) &&
						Integer.parseInt( d ) > 28 && m.equals( "February" ) ) 
					resultField.setText( "Year is not leap!" );
				else if ( Integer.parseInt( yearField.getText() ) < 1900 ) 
					resultField.setText( "Year must be >= 1900." );
				else {
					result = classObject.calculateDay();
					resultField.setText( "Fell/falls on a " + result );
				}
			} catch ( NumberFormatException exc ) {
				result = "Only numerical data please!";
				resultField.setText( result );
			}
		}
		else if ( e.getSource() == exitButton ) System.exit( 0 );
		else if ( e.getSource() == resetButton ) {
			resultField.setText( "" );
			yearField.setText( "" );
			d = "1"; m = "January";
			dayValues.setSelectedIndex( 0 );
			monthValues.setSelectedIndex( 0 );
		}
		else if ( e.getSource() == dayValues ) {
			d = ( String ) dayValues.getSelectedItem();
		}
		else if ( e.getSource() == monthValues ) {
			m = ( String ) monthValues.getSelectedItem();
		}
	}
	
	public static void main( String[] args ) { 
		new ApplicationDemo(); 
	}
}