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The Java 2D™ API provides several classes
that define common geometric objects, such as points, lines,
curves, and rectangles. These new geometry classes are part of the
java.awt.geom package. For backward
compatibility, the geometry classes that existed in previous
versions of the JDK software, such as Rectangle, Point, and
Polygon, remain in the java.awt package.
The Java 2D API geometries such as GeneralPath, Arc2D, and
Rectangle2D implement the Shape interface defined in java.awt. Shape provides
a common protocol for describing and inspecting geometric path
objects. A new interface, PathIterator,
defines methods for retrieving elements from a geometry.
Using the geometry classes, you can easily define and manipulate virtually any two-dimensional object.
The following tables list the key geometry
interfaces and classes. Most of these interfaces and classes are
part of the java.awt.geom package. Some,
like Shape, are part of the java.awt package, primarily to maintain backward
compatibility with earlier versions of the JDK software.
A Shape is an instance of any class that implements
the Shape interface, such as
GeneralPath or Rectangle2D.Float. A Shape’s contour (outline) is referred to as
its path.
When a Shape is drawn,
the pen style defined by the Stroke
object in the Graphics2D context is
applied to the Shape’s path. When
a Shape is filled, the Paint in the Graphics2D
context is applied to the area within its path. For more
information, see “Rendering
with Graphics2D” on page 15.
A Shape’s path
can be also used to define a clipping
path. A clipping path determines what pixels are
rendered—only those pixels that lie within the area defined
by the clipping path are rendered. The clipping path is part of the
Graphics2D context. For more
information, see “Setting the
Clipping Path” on page 32.
A GeneralPath is a
shape that can be used to represent any two-dimensional object that
can be constructed from lines and quadratic or cubic curves. For
convenience, java.awt.geom provides
additional implementations of the Shape
interface that represent common geometric objects such as
rectangles, ellipses, arcs, and curves. The Java2D™ API also
provides a special type of shape that supports constructive area
geometry.
Constructive Area Geometry (CAG) is the process of
creating new geometric objects by performing boolean operations on
existing objects. In the Java 2D API, a special type of
Shape called an Area supports boolean operations. You can construct
an Area from any Shape.
Areas support the
following Boolean operations:
These operations are illustrated in Figure 3-1.

A bounding box is a rectangle that fully encloses a shape’s geometry. Bounding boxes are used to determine whether or not an object has been selected or “hit” by the user.
The Shape interface
defines two methods for retrieving a shape’s bounding box,
getBounds and getBounds2D. The getBounds2D method returns a Rectangle2D instead of a Rectangle, providing a higher-precision description
of the shape’s bounding box.
Shape also provides
methods for determining whether or not:
contains)contains)intersects)Areas can be used to
quickly construct complex Shapes from
simple shapes such as circles and squares. To create a new complex
Shape by combining Areas:
Shapes, construct the
Areas to be combined.add, subtract,
intersect, exclusiveOr.For example, CAG could be used to create a pear
like that shown in Figure 3-2.

The body of the pear is constructed by performing
a union operation on two overlapping Areas: a circle and an oval. The leaves are each
created by performing an intersection on two overlapping circles
and then joined into a single Shape
through a union operation. Overlapping circles are also used to
construct the stem through two subtraction operations.
You can implement the Shape interface to create a class that defines a new
type of shape. It doesn’t matter how you represent the shape
internally, as long as you can implement the Shape interface methods. The Shape must be able to generate a path that specifies
its contour.
For example, you could create a simple
implementation of Shape that represents
polygons as arrays of points. Once the polygon is built, it could
be passed to draw, setClip, or any other method that expects a
Shape object as an argument.
The PolygonPath class
must implement the Shape interface
methods:
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