The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
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Constructive area geometry (CAG) is the process of creating new geometric shapes by performing boolean operations on existing ones. In the Java 2D API the
Area
class implements the
Shape
interface and supports the following boolean operations.
Union | Subtraction | ||
Intersection | Exclusive-or (XOR ) |
In this example Area
objects construct a pear shape from several ellipses.
contains the complete code for this applet.Pear.java
The leaves are each created by performing an intersection on two overlapping circles.
leaf = new Ellipse2D.Double(); ... leaf1 = new Area(leaf); leaf2 = new Area(leaf); ... leaf.setFrame(ew-16, eh-29, 15.0, 15.0); leaf1 = new Area(leaf); leaf.setFrame(ew-14, eh-47, 30.0, 30.0); leaf2 = new Area(leaf); leaf1.intersect(leaf2); g2.fill(leaf1); ... leaf.setFrame(ew+1, eh-29, 15.0, 15.0); leaf1 = new Area(leaf); leaf2.intersect(leaf1); g2.fill(leaf2);
Overlapping circles are also used to construct the stem through a subtraction operation.
stem = new Ellipse2D.Double(); ... stem.setFrame(ew, eh-42, 40.0, 40.0); st1 = new Area(stem); stem.setFrame(ew+3, eh-47, 50.0, 50.0); st2 = new Area(stem); st1.subtract(st2); g2.fill(st1);
The body of the pear is constructed by performing a union operation on a circle and an oval.
circle = new Ellipse2D.Double(); oval = new Ellipse2D.Double(); circ = new Area(circle); ov = new Area(oval); ... circle.setFrame(ew-25, eh, 50.0, 50.0); oval.setFrame(ew-19, eh-20, 40.0, 70.0); circ = new Area(circle); ov = new Area(oval); circ.add(ov); g2.fill(circ);