Swing Hacks

Display Dates in a Custom Calendar #4

Chapter 1, Basic JComponents

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21

HACK

This loads the images in the constructor and sets up date formatters for the

month, year, and day. Override the

paintComponent( ) method to turn on

anti-aliasing, draw the background, and then draw the month and year for

the current date.

You’ll notice that there is a default date in case the devel-

oper doesn’t set one (always a good practice).

Draw the Days of the Month

The java.util.Calendar object handles all date calculations, so let’s start

there. You’ll need two calendars: one to represent the current date (

today)

and one that you update as you loop through the grid of dates (

cal). Here’s

what that looks like in code:

Calendar today = Calendar.getInstance( );

today.setTime(date);

Calendar cal = Calendar.getInstance( );

cal.setTime(date);

protected SimpleDateFormat year = new SimpleDateFormat("yyyy");

protected SimpleDateFormat day = new SimpleDateFormat("d");

protected Date date = new Date( );

public void setDate(Date date) {

this.date = date;

}

public CalendarHack( ) {

background = new ImageIcon("calendar.png").getImage( );

highlight = new ImageIcon("highlight.png").getImage( );

day_img = new ImageIcon("day.png").getImage( );

this.setPreferredSize(new Dimension(300,280));

}

public void paintComponent(Graphics g) {

((Graphics2D)g).setRenderingHint(RenderingHints.KEY_ANTIALIASING,

RenderingHints.VALUE_ANTIALIAS_ON);

g.drawImage(background,0,0,null);

g.setColor(Color.black);

g.setFont(new Font("SansSerif",Font.PLAIN,18));

g.drawString(month.format(date),34,36);

g.setColor(Color.white);

g.drawString(year.format(date),235,36);

}

}

Example 1-9. A Calendar base component (continued)

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Chapter 1, Basic JComponents

#4 Display Dates in a Custom Calendar

HACK

cal.set(Calendar.DATE,1);

cal.add(Calendar.DATE,-cal.get(Calendar.DAY_OF_WEEK)+1);

for(int week = 0; week < 6; week++) {

for(int d = 0; d < 7; d++) {

Image img = day_img;

Color col = Color.black;

// only draw if it's actually in this month

if(cal.get(Calendar.MONTH) == today.get(Calendar.MONTH)) {

if(cal.equals(today)) {

img = highlight;

col = Color.white;

}

g.drawImage(img,d*30+46,week*29+81,null);

g.drawString(day.format(cal.getTime( )),

d*30+46+4,week*29+81+20);

}

cal.add(Calendar.DATE,+1);

}

}

You’ll notice that both calendars are initialized to date, but then the code

resets

cal’s date to the first of the month and subtracts the current day of the

week. This has the effect of setting

cal to the last Sunday before (or equal to)

the real current date. You have to perform this calculation because you need

to start drawing in the upper-lefthand corner of the calendar grid, which will

almost always include a few days from the previous month. Once all of that

is done, the code loops through each week and draws each day.

Now, here’s the tricky part:

cal goes back seven days, which is almost cer-

tainly going to run back into the previous month. Because the calendar is

month-based, those days in the previous month shouldn’t be drawn. That’s

why there is a check to see if

cal’s month is equal to today’s month. If they

are equal, then you can draw the day safely; if not, skip drawing and just

increment the date.

The last thing to check is if the current day in

cal is equal to the real current

date. If it is, you want to use a different color and background image

(

highlight). Finally, the image and day numbers are drawn, with the posi-

tion determined by the current day of the week and week number. You can

adjust the multipliers and offsets (

30, 46, 29, 81) to suit your taste. The

drawString( ) method has a few extra pixels of padding to make the day

number appear more centered in the day image.

And now you have a completely custom calendar, suitable for placement

within the zaniest of interfaces.