Processing: Creative Coding and Computational Art

Inheritance in Java is absolutely fundamental to the language’s design. In fact, every class
in Java except the Object class has at a minimum one superclass, and every class except
the Object class has a lineage that goes back to Object. For example, when you export a
Processing sketch, a Java applet is created. Here is the Applet class’s lineage:
java.lang.Object
java.awt.Component
java.awt.Container
java.awt.Panel
java.applet.Applet
The classes are the words that start with an initial cap (Object, Component, Container,
Panel, and Applet). The words connected to them by a dot are the packages the classes
live in. Packages are just directories or folders that hold class files. In this lineage, Applet
inherits from Panel, which inherits from Container, which inherits from Component, which
inherits from Object. Therefore, the Applet class has access to all the accessible properties
and methods declared within its own class and from all the classes above it—giving the
Applet class access to over 200 methods. However, the inheritance chain doesn’t go the
other way. Object doesn’t have access to any properties or methods besides those
declared within its own class description, as it is at the top of the inheritance chain for all
classes. On the other hand, the Panel class has access to methods/properties in
Container, Component, and Object—but not Applet.
Applying inheritance
Using inheritance is pretty straightforward. In the following example, I have a very simple
Shape class and Polygon class. The Polygon class inherits from (or extends) the Shape class.
class Shape {
//class properties
int x;
int y;
int w;
int h;
//constructors
Shape (){
}
Shape (int x, int y, int w, int h){
this.x = x;
this.y = y;
this.w = w;
this.h = h;
}
}
class Polygon extends Shape{
int pts;
//constructor
OBJECT-ORIENTED PROGRAMMING
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