Java Foundation Classes in a Nutshell

Note that these calls to rotate() rotate the coordinate system about the origin.

Ther e is also a three-argument version of the method that rotates about a specified

point, which can often be more useful.

The final transformation method defined by

Graphics2D is shear(). The effects of

this method are not as intuitive as the methods we’ve already discussed. After a

call to

shear(), any rectangles you draw appear skewed, as parallelograms.

Any calls you make to

translate(), scale(), rotate(), and shear() have a

cumulative effect on the mapping from user space to device space. This mapping

is encapsulated in a

java.awt.geom.AffineTransform object and is one of the

graphics attributes maintained by a

Graphics2D object. You can obtain a copy of

the current transform with

getTransform(), and you can set a transform dir ectly

with

setTransform(). setTransform() is not cumulative. It simply replaces the

curr ent user-to-device-space mapping with a new mapping:

AffineTransform t = g.getTransform(); // Save the current transform

g.rotate(theta); // Change the transform

g.drawRect(100, 100, 200, 200); // Draw something

g.setTransform(t); // Restore the transform to its old state

AffineTransform is used in a number of places in the Java 2D API; we’ll discuss it

in more detail later in this chapter. Once you understand the details and some of

the math behind this class, you can define

AffineTransform objects of your own ...