java awt printable and print

Question

I wanted to print what is on the canvas and came across this suggested code: //https://www.cis.upenn.edu/~bcpierce/courses/629/jdkdocs/guide/awt/designspec/printing.html

PrintJob pjob = getToolkit().getPrintJob(new Frame(), "Print TimeGraph", null);
if(pjob !=null) {
    Graphics pg = pjob.getGraphics();
    if (pg != null) {
        canvas.printAll(pg);
        pg.dispose();   // flush page
    }
        pjob.end();
    }

Then in the canvas paint method:

@Override
public void paint(Graphics g) {
    if(g instanceof PrintGraphics){
       if(graphTitle != null){
          g.drawString ("Hello Printer",left+10,top+50);
        } 
    }
}

It printed but some of the margins were cut off. I read that awt.printable enabled better margin control so I changed the code to:

PrinterJob pj = PrinterJob.getPrinterJob();
PageFormat pf = pj.defaultPage();
Paper paper = new Paper();
double margin = 4.5; 
paper.setImageableArea(margin, margin, paper.getWidth() - margin * 2, paper.getHeight() - margin * 2);
pf.setPaper(paper);
pj.setPrintable(new MyPrintable(), pf);
if (pj.printDialog()) {
    try {
        pj.print();
    } catch (PrinterException pp) {
        System.out.println(pp);
    }
}

and

class MyPrintable implements Printable {
    public int print(Graphics g, PageFormat pf, int pageIndex) {
        if (pageIndex != 0)
          return NO_SUCH_PAGE;
    Graphics2D g2 = (Graphics2D) g;
    g2.translate(pf.getImageableX(), pf.getImageableY());
    canvas.printAll(g);
    return PAGE_EXISTS;
    }

}

And that solved the margin issue. The problem is that I no longer get an instanceof PrintGraphics in the paint event. Its always a Graphics object an there is no way to print additional information when paint is invoked from printing. I tried casting the Graphics object to a PrintGraphics object in the canvas.printAll method to no avail. How can I regain the ability to differentiate what called the paint method either by checking the object type or by some other means?

Answer 1

Perhaps hackish but an indirection with extra parameter, on the line of the code below, may solve your problem for the moment.

class MyCanvas {
  protected void doPaint(Graphics g, boolean forPrinter) {
    if(forPrinter){
       if(graphTitle != null){
          g.drawString ("Hello Printer",left+10,top+50);
        } 
    }
  }

  @Override
  public void paint(Graphics g) {
    this.doPaint(g, false);
  }
}

class MyPrintable implements Printable {
    public int print(Graphics g, PageFormat pf, int pageIndex) {
      if (pageIndex != 0)
          return NO_SUCH_PAGE;
      Graphics2D g2 = (Graphics2D) g;
      g2.translate(pf.getImageableX(), pf.getImageableY());

      // If on many pages, this will need to be handled better.
      // But as are ignoring the pageIndex, I assume 
      // you are on a single page and pleased to print everything on it
      canvas.doPaint(g, true);
      return PAGE_EXISTS;
    }
}

PS: unless you really want to have a "composite printable" it is much better to make you MyCanvas implement the Printable interface itself.
This implies: move the public int print(Graphics g, PageFormat pf, int pageIndex) inside the MyCanvas class itself - cannot hurt and it helps if you want to print something you compute using the MyCanvas non-public members.