Graphics and Java 2D - Java: How to Program Early Objects - page 584

Fig. 13.30 | Testing ShapesJPanel . (Part 2 of 2.)
Ovals, Gradient Fills and Paint Objects
The first shape we draw is an oval filled with gradually changing colors . Lines 28-29 invoke
Graphics2D method setPaint to set the Paint object that determines the color for the
shape to display. A Paint object implements interface java.awt.Paint . It can be some-
thing as simple as one of the predeclared Color objects introduced in Section 13.3 (class
Color implements Paint ), or it can be an instance of the Java 2D API's GradientPaint ,
SystemColor , TexturePaint , LinearGradientPaint or RadialGradientPaint classes. In
this case, we use a GradientPaint object.
Class GradientPaint helps draw a shape in gradually changing colors —called a gra-
dient . The GradientPaint constructor used here requires seven arguments. The first two
specify the starting coordinates for the gradient. The third specifies the starting Color for
the gradient. The fourth and fifth specify the ending coordinates for the gradient. The
sixth specifies the ending Color for the gradient. The last argument specifies whether the
gradient is cyclic ( true ) or acyclic ( false ). The two sets of coordinates determine the
direction of the gradient. Because the second coordinate (35, 100) is down and to the right
of the first coordinate (5, 30), the gradient goes down and to the right at an angle. Because
this gradient is cyclic ( true ), the color starts with blue, gradually becomes yellow, then
gradually returns to blue. If the gradient is acyclic, the color transitions from the first color
specified (e.g., blue) to the second color (e.g., yellow).
Line 30 uses Graphics2D method fill to draw a filled Shape object—an object that
implements interface Shape (package java.awt ). In this case, we display an
Ellipse2D.Double object. The Ellipse2D.Double constructor receives four arguments
specifying the bounding rectangle for the ellipse to display.
Rectangles, Stroke s
Next we draw a red rectangle with a thick border. Line 33 invokes setPaint to set the
Paint object to Color.RED . Line 34 uses Graphics2D method setStroke to set the char-
acteristics of the rectangle's border (or the lines for any other shape). Method setStroke
requires as its argument an object that implements interface Stroke (package java.awt ).
In this case, we use an instance of class BasicStroke . Class BasicStroke provides several
constructors to specify the width of the line, how the line ends (called the end caps ), how
lines join together (called line joins ) and the dash attributes of the line (if it's a dashed
line). The constructor here specifies that the line should be 10 pixels wide.
Line 35 uses Graphics2D method draw to draw a Shape object—in this case, a
Rectangle2D.Double . The Rectangle2D.Double constructor receives arguments speci-
fying the rectangle's upper-left x -coordinate, upper-left y -coordinate, width and height.