Printing in Java - An Introduction to Graphical User Interfaces with Java Swing - page 228

the runtime system will not call print again. The programmer has to make
sure that the correct value is returned. This way multi-page documents can be
printed.
Let us now look at a simple implementation of the interface Printable .We
implement method print such that it prints only one page; our panel is a one-page
document. We first check whether the parameter pageIndex is 0 (the first page). If
so we call the paint -method of the panel and return PAGE_EXISTS .If pageIndex is
greater than 0 we return NO_SUCH_PAGE . The runtime system will then stop calling
print .
Let us analyse what is happening in the first case, i.e. when pageIndex is 0.
By calling the paint -method of the panel, a repainting is initiated. The painting is
done on some device. Which device this is (the screen or the printer) is determined
by the Graphics object. In our example we pass the Graphics object g which we
receive as an argument of print on to the paint method. This object is generated
by the runtime system and refers to some printer. As a result, paint draws to
the printer and not to the screen. We cannot use repaint here because it does
not allow a Graphics object to be passed as an argument; repaint initiates a
redrawing of the screen. The skeleton of the implementation then looks like this:
public int print(Graphics g, PageFormat pageFormat, int pageIndex) {
if (pageIndex > 0)
{
return (NO_SUCH_PAGE);
}
else
{
this .paint(g);
return (PAGE_EXISTS);
}
}
There are, however, some technical precautions to be taken. First of all one should
switch off the double buffering of the graphics. This feature is important for a nice
display when the screen is redrawn but might spoil the printing. After the printing,
the double buffering should be switched on again. We therefore surround the paint
command by some commands as shown below. We do not elaborate on the class
RepaintManager used here:
RepaintManager currentManager = RepaintManager.currentManager( this );
currentManager.setDoubleBufferingEnabled( false );
paint(g);
currentManager.setDoubleBufferingEnabled( true );
Another topic to consider when printing is the placement and scaling of the printed
image. The origin of the printer coordinate system is normally the upper left
corner of the paper . Most printers, however, cannot print on some small margin
of the paper for technical reasons. Therefore the upper left corner of the printable
area of the paper is below and to the right of its upper left corner. The Graphics