Java中Printable接口在哪里设置打印内容？

public int print(Graphics gra, PageFormat pf, int pageIndex) throws PrinterException {
       System.out.println("pageIndex="+pageIndex);
       Component c = null;
      switch(pageIndex){
         case 0:
//我在这里处理gra对象的相应处理，画出了一个图像
         return PAGE_EXISTS;
         default:
         return NO_SUCH_PAGE;
      }
现在的问题是我调用打印功能：
    book.append(new PrintTest(), pf);
     PrinterJob job = PrinterJob.getPrinterJob();
     job.setPageable(book);
但是new PrintTest()实例了有什么用？我打印出来的是白纸啊！在什么地方进行打印图像的设置呢？有没有不要利用Frame或者Compent的例子？ java 打印 PrinterJob Printable --------------------编程问答--------------------

import java.awt.Color;

import java.awt.Font;

import java.awt.Graphics;

import java.awt.Graphics2D;

import java.awt.geom.Rectangle2D;

import java.awt.print.PageFormat;

import java.awt.print.Paper;

import java.awt.print.Printable;

import java.awt.print.PrinterException;

import java.awt.print.PrinterJob;



public class PrintableDemo implements Printable {

  public int print(Graphics g, PageFormat pf, int pageIndex) {

    if (pageIndex != 0)

      return NO_SUCH_PAGE;

    Graphics2D g2 = (Graphics2D) g;

    g2.setFont(new Font("Serif", Font.PLAIN, 36));

    g2.setPaint(Color.black);

    g2.drawString("Java Source and Support", 100, 100);

    Rectangle2D outline = new Rectangle2D.Double(pf.getImageableX(), pf

        .getImageableY(), pf.getImageableWidth(), pf

        .getImageableHeight());

    g2.draw(outline);

    return PAGE_EXISTS;

  }

  public static void main(String[] args) {

    PrinterJob pj = PrinterJob.getPrinterJob();



    PageFormat pf = pj.defaultPage();

    Paper paper = new Paper();

    double margin = 36; // half inch

    paper.setImageableArea(margin, margin, paper.getWidth() - margin * 2,

        paper.getHeight() - margin * 2);

    pf.setPaper(paper);



    pj.setPrintable(new PrintableDemo(), pf);

    if (pj.printDialog()) {

      try {

        pj.print();

      } catch (PrinterException e) {

        System.out.println(e);

      }

    }

  }

}

补充：Java ,  Java SE