org.jfree.report

Some rules when working with the report definition objects:

• Functions cannot be added to the report once the report generation has started.
• Do not modify the report structure after the report generation is started, unless you know exactly what you are doing.
• It is safe to modify the report definition before the report is started.
• Once the report processing has started, the report from the report processor must not be reused for other purposes.

Groups

A group is a set of database rows, where the contents of the group fields are equal for all rows.

Lets look at the following table:

Car	Color	Price
Toyota	blue	10.000
Toyota	blue	20.000
Toyota	red	15.000
Lexus	blue	25.000
Lexus	yellow	15.000
BMW	yellow	40.000
BMW	blue	35.000
BMW	green	5.000

Groups are always defined on sorted tables. A group is defined by selecting one or more rows, which should form the group. A group instance will contain all rows from the beginning of the group until one of the group fields changes.

Lets select the row car for our group:

Selecting that row as group argument will result in 3 group instances. The first group instance will contain the first 3 rows (as the contents of these rows are equal).

The next instance will contain all rows of the "Lexus" car and the last group contains all rows from the "BMW" rows.

If a group is defined by more than one field, then the group will end, if one of the group member fields changes.

Lets define a group which consists of "Car" and "Color".

The first instance of the group will contain the first 2 rows (Toyota,blue). Then the value in the column "Color" changes, so a new group instance is started. This new group contains a single row, as the column "Car" in the next row will contain a different value.

The next two group instances are "Lexus, blue" and "Lexus, yellow", both group instances contain 1 row, as the color changes after 1 row.

The next row starts a new group, as the column "Car" contains a different value (BWM instead of Lexus). It doesn't matter, that the color is still equal, to end a group instance, it is sufficient that one column value changed.

In HTML anchors would be produced by using <a name="anchorname">.

Elements can either be Bands (which are container classes that group elements) or content-elements.

The ImageContainer is the common base interface for the URLImageContainer (which references remote images) and the LocalImageContainer (which references local AWT-Image instances).

All the layouting engine needs to know about images, are the image dimensions and the possible scale factor for the contained image.

Page oriented reports use the page definition to distribute the content of one logical page to the physical pages. The order of the physical pages in the page definition defines the content order in the generated documents.

Flow oriented reports will use the page-definitions width as default width for the layouting.

If a logical page is completly empty, it will be removed from the report and a pageCanceled event is fired.

Note that if there is a page footer on the last page of your report, it will be printed below the report footer, the logic being that the page footer *always* appears at the bottom of the page.

A flag can be set forcing the report generator to start a new page after printing the report header.

Note that if there is a page header on the first page of your report, it will be printed above the report header, the logic being that the page header *always* appears at the top of the page.

All content is converted to String using the String.valueOf () method.