Practical Coding in Java

//
// HelloProcessing.java
//


//
// Notes:
//
// 1) The import statement is required to use Processing classes.
// 
// 2) When you are in Processing, everything is "global":  setup(),
// draw(), all variables declared outside those functions.  In
// reality, there is an enclosing PApplet class, of which setup()
// and draw() are member functions.  Any "global" variables in
// Processing are actually member variables of your PApplet.
//
// 3) Your main class is actually a sub-class of (extends) PApplet.
// This means that it inherits all of the PApplet member functions
// (i.e. size(), fill(), ellipse()), but also allows you to override
// (write your own) setup() and draw() functions.
//
// 4) There is a settings() function in addition to a setup()
// function, for some technical issue in Processing.  Put your
// size() call in settings(), and all other initialization in
// setup().
//
// 5) To run your program, your main() function must call the
// PApplet.main() function with the name of your class as an
// argument.
//


import processing.core.*; // 1


public class HelloProcessing extends PApplet // 2, 3
{
    public void settings() // 4
    {
        size(400, 400);
    }

    public void setup()
    {
        x = 0;        
    }

    public void draw()
    {
        background(0);
        ellipse(x, 200, 100, 50);
        x++;
    }

    private float x; // 2

    public static void main(String[] args)
    {
        PApplet.main("HelloProcessing"); // 5
    }
}