[Chapter 17] 17.2 PrintJob Class

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| Chapter 17 Printing |

## 17.2 PrintJob Class

The abstract `PrintJob` class provides the basis for the platform-specific printing subclasses. Through `PrintJob`, you have access to properties like page size and resolution.

### Constructor and Pseudo-Constructor

public PrintJob ()

  The `PrintJob()` constructor is public; however, the class is abstract, so you would never create a `PrintJob` instance directly.

Since you can't call the `PrintJob` constructor directly, you need some other way of getting a print job to work with. The proper way to get an instance of `PrintJob` is to ask the `Toolkit`, which is described in Chapter 15, Toolkit and Peers. The `getPrintJob()` method requires a `Frame` as the first parameter, a `String` as the second parameter, and a `Properties` set as the third parameter. Here's how you might call it:

    PrintJob pjob = getToolkit().getPrintJob(aFrame, "Job Title",
                                             (Properties)null);

The `Frame` is used to hold a print dialog box, asking the user to confirm or cancel the print job. (Whether or not you get the print dialog may be platform specific, but your programs should always assume that the dialog may appear.) The `String` is the job's title; it will be used to identify the job in the print queue and on the job's header page, if there is one.

The `Properties` parameter is used to request printing options, like page reversal. The property names, and whether the requested properties are honored at all, are platform specific. UNIX systems use the following properties:

`awt.print.printer`
`awt.print.paperSize`
`awt.print.destination`
`awt.print.orientation`
`awt.print.options`
`awt.print.fileName`
`awt.print.numCopies`

Windows NT/95 ignores the properties sheet. If the properties sheet is `null`, as in the previous example, you get the system's default printing options. If the properties sheet is non-`null`, `getPrintJob()` modifies it to show the actual options used to print the job. You can use the modified properties sheet to find out what properties are recognized on your system and to save a set of printing options for use on a later print job.

If you are printing multiple pages, each page should originate from the same print job.

According to Sun's documentation, `getPrintJob()` ought to return `null` if the user cancels the print job. However, this is a problem. On some platforms (notably Windows NT/95), the print dialog box doesn't even appear until you call the `getGraphics()` method. In this case, `getPrintJob()` still returns a print job and never returns `null`. If the user cancels the job, `getGraphics()` returns `null`.

### Methods

public abstract Graphics getGraphics ()

  The `getGraphics()` method returns an instance of `Graphics` that also implements `PrintGraphics`. This graphics context can then be used as the parameter to methods like `paint()`, `print()`, `update()`, or `printAll()` to print a single page. (All of these methods result in calls to `paint()`; in `paint()`, you draw whatever you want to print on the `Graphics` object.)

  On Windows NT/95 platforms, `getGraphics()` returns `null` if the user cancels the print job.

public abstract Dimension getPageDimension ()

  The `getPageDimension()` method returns the dimensions of the page in pixels, as a `Dimension` object. Since `getGraphics()` returns a graphics context only for a single page, it is the programmer's responsibility to decide when the current page is full, print the current page, and start a new page with a new `Graphics` object. The page size is chosen to roughly represent a screen but has no relationship to the page size or orientation.

public abstract int getPageResolution ()

  The `getPageResolution()` method returns the number of pixels per inch for drawing on the page. It is completely unclear what this means, since the number returned has no relationship to the printer resolution. It appears to be similar to the screen resolution.

public abstract boolean lastPageFirst ()

  The `lastPageFirst()` method lets you know if the user configured the printer to print pages in reverse order. If this returns `true`, you need to generate the last page first. If `false`, you should print the first page first. This is relevant only if you are trying to print a multipage document.

public abstract void end ()

  The `end()` method terminates the print job. This is the last method you should call when printing; it does any cleaning up that's necessary.

public void finalize ()

  The `finalize()` method is called by the garbage collector. In the event you forget to call `end()`, `finalize()` calls it for you. However, it is best to call `end()` as soon as you know you have finished printing; don't rely on `finalize()`.

PrintGraphics Interface |  | Component Methods