GUI of a calendar (monthly)

Question

I tried to built a GUI for a Kalender but i need explanation with comments to understand the code. Can someone help me?
I work with this code, it is form this forum (post at the end of line):
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.text.*;
public class MightyMouse1
     static class SimpleCalendar
          extends JPanel
          private static final String[] sDays=
               new DateFormatSymbols().getWeekdays();
          private static int sStartDay= 0;
          static {
               for (int i= 0; i< sDays.length; i++)
                    if (sDays.length() <= 0)
                         sStartDay++;
          private static final int[] sMonthDays=
               {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
          private Calendar mDate;
          private int mCellWidth= 1;
          private int mCellHeight= 1;
          private int mStartDay;
          private int mDaysInMonth;
          public SimpleCalendar()
               mDate= Calendar.getInstance();
               addMouseListener(new MouseAdapter() {
                    public void mouseClicked(MouseEvent e) {
                         hitTest(e.getPoint());
                         e.consume();
          public void setDate(Date date)
               mDate.setTime(date);
               repaint();
          public Date getDate() { return mDate.getTime(); }
          public Dimension getPreferredSize() { return getMinimumSize(); }
          public Dimension getMinimumSize() { return new Dimension(180,180); }
          public void paint(Graphics g)
               g.clearRect(0, 0, getSize().width, getSize().height);
               doMonth(g);
          private void hitTest(Point p)
               int cellX, cellY, dom;
               cellX= (int) p.x / mCellWidth;
               cellY= (int) p.y / mCellHeight;
               if (cellY != 0) { // not the days title bar
                    dom= cellX+1+((cellY-1)*7)-mStartDay;
                    if (dom > 0 && dom <= mDaysInMonth) {
                         mDate.set(Calendar.DAY_OF_MONTH, dom);
                         setDate(mDate.getTime());
          private boolean leapYear(int year)
               if ((year % 400) == 0)
                    return(true);
               if ((year > 1582) && ((year % 100) == 0))
                    return(false);
               if ((year % 4) == 0)
                    return(true);
               return(false);
          private void drawMonth(Graphics g, int startDay, int days, boolean special)
               mStartDay= startDay;
               mDaysInMonth= days;
               mCellWidth= getSize().width / 7;
               mCellHeight= getSize().height / 7;
               int day= mDate.get(Calendar.DAY_OF_MONTH);
               FontMetrics metrics= g.getFontMetrics();
               // Draw the days of the week (M, T, W ...) on the top line
               for (int col= 0, x= 0, y= 0; col < 7; col++) {
                    String s= String.valueOf(sDays[col+sStartDay].charAt(0));
                    // Make (x,y) the top left of the cell
                    x= col * mCellWidth;
                    y= 0;
                    // Make (x,y) the center of the cell
                    x= x + (mCellWidth/2);
                    y= y + (mCellHeight/2);
                    // Move (x,y) to accomodate the text
                    x= x - (metrics.stringWidth(s)/2);
                    y= y + (metrics.getAscent()/2);
                    g.setColor(Color.blue);
                    g.drawString(s, x, y);
               // Draw the days of the month starting one line down
               for (int i= 1, row= 1, col= startDay, x= 0, y= 0; i <= days; i++) {
                    if (special && (i == 5))
                         i += 10; // skip 10 days (Oct 5-14) in October, 1582
                    String s= "" + i;
                    // Make (x,y) the top left of the cell
                    x= col * mCellWidth;
                    y= row * mCellHeight;
                    if (i == day) {
                         g.setColor(new Color(255,255,200));
                         g.fillRect(x, y, mCellWidth, mCellHeight);
                    // Make (x,y) the center of the cell
                    x= x + (mCellWidth/2);
                    y= y + (mCellHeight/2);
                    // Move (x,y) to accomodate the text
                    x= x - (metrics.stringWidth(s)/2);
                    y= y + (metrics.getAscent()/2);
                    g.setColor(Color.black);
                    g.drawString(s, x, y);
                    col++;
                    if (col > 6) {
                         col= 0;
                         row++;
          private void doMonth(Graphics g)
               int month= mDate.get(Calendar.MONTH);
               int year= mDate.get(Calendar.YEAR);
               int daysInMonth;
               int startOfMonth;
               int y= year - 1;
               boolean leap= leapYear(year);
               boolean special= ((year == 1582) && (month == 9));
               boolean pre= ((year < 1582) || ((year == 1582) && (month <= 9)));
               if (pre)
                    startOfMonth = 6 + y + (y/4);
               else
                    startOfMonth = 1 + y + (y/4) - (y/100) + (y/400);
               if (leap && month == 1)
                    daysInMonth= 29;
               else
                    daysInMonth= sMonthDays[month];
               for (int i = 0; i < month; i++)
                    startOfMonth += sMonthDays[i];
               drawMonth(g, startOfMonth % 7, daysInMonth, special);
     static class FancyCalendar
          extends JPanel
          private static final String[] sMonths=
               new DateFormatSymbols().getMonths();
          private JComboBox mComboMonths;
          private JComboBox mComboYears;
          private JLabel mLabel;
          private SimpleCalendar mCalendar;
          private int mSelectedMonth;
          private int mSelectedYear;
          private Dimension mMinimumSize;
          private int mFirstYear;
          private int mLastYear;
          private Date mDate;
          private boolean mShowTime;
          public FancyCalendar() { this(-10, 10); }
          public FancyCalendar(int firstYear, int lastYear)
               mFirstYear= firstYear;
               mLastYear= lastYear;
               adjustYears();
               setLayout(new BorderLayout(2,2));
               mCalendar= new SimpleCalendar();
               add(mCalendar, BorderLayout.CENTER);
               setupCombos();
               setDate(mCalendar.getDate());
          public void setDate(Date date)
               mDate= date;
               mCalendar.setDate(date);
               Calendar cal= Calendar.getInstance();
               cal.setTime(date);
               mSelectedMonth= date.getMonth();
               mSelectedYear= cal.get(Calendar.YEAR);
               mComboYears.setSelectedIndex(mSelectedYear-mFirstYear);
               mComboMonths.setSelectedIndex(mSelectedMonth);
          public Date getDate() { return mDate; }
          public Dimension getPreferredSize() { return getMinimumSize(); }
          public Dimension getMinimumSize() { return mMinimumSize; }
          private void adjustYears()
               Date today= new Date();
               if (mFirstYear < 0 && mFirstYear >= -50)
                    mFirstYear= 1900+ today.getYear() +mFirstYear;
               if (mLastYear > 0 && mLastYear <= 50)
                    mLastYear= 1900+ today.getYear() +mLastYear;
               if (mFirstYear < 1900)
                    mFirstYear= 1900;
          private void setupCombos()
               mMinimumSize= new Dimension(170,180);
               JPanel p= new JPanel();
               mComboMonths= new JComboBox(sMonths);
               mComboYears= new JComboBox();
               p.add(mComboMonths);
               p.add(mComboYears);
               add(p, BorderLayout.NORTH);
               for(int i= mFirstYear; i<= mLastYear; i++)
                    mComboYears.addItem(""+i);
               mComboMonths.addActionListener(new ActionListener() {
                    public void actionPerformed(ActionEvent e)
                         if(mComboMonths.getSelectedIndex() != mSelectedMonth) {
                              mSelectedMonth= mComboMonths.getSelectedIndex();
                              Calendar cal= Calendar.getInstance();
                              cal.setTime(getDate());
                              cal.set(Calendar.MONTH, mSelectedMonth);
                              setDate(cal.getTime());
               mComboYears.addActionListener(new ActionListener() {
                    public void actionPerformed(ActionEvent e)
                         int y= mComboYears.getSelectedIndex() +mFirstYear;
                         if((y > 0) && (y != mSelectedYear)) {
                              mSelectedYear= y;
                              Calendar cal= Calendar.getInstance();
                              cal.setTime(getDate());
                              cal.set(Calendar.YEAR, mSelectedYear);
                              setDate(cal.getTime());
                              // If date was feb 29 and new year is not leap,
                              // then the month will have moved on one, so re-set
                              // the combo box
                              mComboMonths.setSelectedIndex(
                                   cal.get(Calendar.MONTH));
public static void main(String[] argv)
JFrame frame= new JFrame();
frame.getContentPane().add(new FancyCalendar());
frame.pack();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
It is from the forum here:
http://forum.java.sun.com/thread.jspa?forumID=31&threadID=
This post:
[Dukes Earned 470] dchsw
Posts:449
Registered: 9/1/98
Re: Developing a calendar
Nov 6, 2003 6:37 AM (reply 3 of 6)

Answer 1

> I tried to built a GUI for a Kalender but i need explanation with comments to understand the code.
http://java.sun.com/docs/books/tutorial/java/index.html
http://java.sun.com/docs/books/tutorial/uiswing/
Let us know if you have a specific question.
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