import java.awt.*;
import java.awt.event.*;
import java.applet.*;

/*This Applet calculates the day of the week for an given date
using Zeller's formula.  For simplicity, dates in the range
1901-1999 are assumed.  (This avoids the millennium bug issue:
years ending in 00 divisible by 4 that are leap years.) Note
that the applet will produce erroneous results if you do not
press the enter key after each entry. */

/*Written for IT 108 by Anne Marchant 1/02.  Developers are advised
that the more modern Swing classes should be used for professional
applications (using JApplet, JButton, JTextField, etc.). However, since 
these require Netscape 6 (or greater) and the Java 2 runtime, and 
these may not be available to all students, the Java 2 AWT has been 
used here. */

public class dayofweekapplet extends Applet implements ActionListener
{
TextField dayField, monthField, yearField;	//User input fields
TextField dayofweek;				//Output field
Button calcButton;				//Control button

static int day=0, month=0, year=0;		//user input
static int century=19;				//Assume 20th century
static int answer=0;				//result

public void init()
{	//We will do our own layout to keep it simple
 	setLayout(null);		
	//Create 3 text fields for input and make them active
	dayField=new TextField(" ");
	dayField.setBounds(200,55,50,25);
        dayField.setEditable(true);
	dayField.addActionListener(this);
        add(dayField);

	monthField=new TextField(" ");
	monthField.setBounds(200,105,50,25);
        monthField.setEditable(true);
	monthField.addActionListener(this);
        add(monthField);

	yearField=new TextField(" ");
	yearField.setBounds(200,155,50,25);
        yearField.setEditable(true);
	yearField.addActionListener(this);
        add(yearField);

	//make a button and activate it
        calcButton=new Button("Calculate");
	calcButton.setBounds(10,200,75,25);
        calcButton.addActionListener(this);
        add(calcButton);

	//create an output text field
	dayofweek=new TextField("");
	dayofweek.setBounds(200,250,200,25);
        dayofweek.setEditable(false);
        add(dayofweek);

	setSize(610,500);
}

//handle user input
public void actionPerformed(ActionEvent e)
{
//get values entered into input fields
   if(e.getSource()==dayField)
	day=(int)Integer.parseInt(dayField.getText().trim());
   if(e.getSource()==monthField)
	month=(int)Integer.parseInt(monthField.getText().trim());
   if(e.getSource()==yearField)
        year=(int)Integer.parseInt(yearField.getText().trim());

//when user presses button, do calculation
 if(e.getActionCommand().equals("Calculate"))
 {

 if (month <= 2)	//adjust values to match formula, since March=1
  {			//if jan or feb, year is previous year
    year -= 1;	
    if (year < 0)	//handle 1900 dates...not really needed for this 
    {			//applet, but useful if we ever expand its 
      year = 99;	//functionality
      century -= 1;
    } 
  }
  if (month > 2) 	// adjust month to match formula Mar=1, Feb=12
    month -= 2;		// if month is March or higher, subtract 2
  else month += 10;	// else, month is Jan. or Feb., so add 10

  answer = get_day_of_week(); //call function to do calculation
  answer = answer%7;   // find specific day of week

//print answer
 switch(answer)
	{
		case 0: dayofweek.setText("Sunday.");
			break;
		case 1: dayofweek.setText("Monday.");
			break;
		case 2: dayofweek.setText("Tuesday.");
			break;
		case 3: dayofweek.setText("Wednesday.");
			break;
		case 4: dayofweek.setText("Thursday.");
			break;
		case 5: dayofweek.setText("Friday.");
			break;
		case 6: dayofweek.setText("Saturday.");
			break;
		default:
			dayofweek.setText("d:"+day+" m:"+month+"y:"+year+
			" c:"+century);
		}

repaint();
}
}  // end get_birthdate()

//Zeller's Rule 
public int get_day_of_week()
{
  int f=0;

  f = day + (13*month-1)/5 + year + year/4 + century/4 - 2*century;

  return f;
}

//Labels for screen
public void paint (Graphics g)
{
	g.drawString("This program determines the day of the week for a given date: 1901-1999.",5,25);
	g.drawString("Press the enter key after each entry:",5,40);
	g.drawString("Enter Day: ",5,65);
	g.drawString("Enter Month: ",5,115);
	g.drawString("Enter last 2 digits of year (01-99):",5,165);
	g.drawString("The day of the week for this date is: ",5,260);
}  // end print_day_of_week

}