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Classes are one of the most important programming constructs in many programming languages. They are the , allowing us to use the object-oriented paradigm to organise code and make it more understandable. Classes are an abstract model or blueprint for an object. An object, like in the real world, can literally be anything, and all objects have properties and functions. And, like the real world, our code can consist almost entirely of interacting objects.

We can also understand classes as extended data types. Unlike the primitive data types we have already looked at, classes define both variables and functions. Programmers call class variables attributes, and class functions function methods, but otherwise, they work pretty much the same as the variables and functions we already know. In order to To get access to these attributes and methods, we need to use a dot syntax, i.e. "." must be placed after the object name, followed by the name of the attribute or the method.

The structure of a class:

class className {

[Attributes - Variables]
[Constructor – Initialising function]

[Methods- Functions]

}

Constructor 

. For example car.speed might store the speed attribute of an object and the car.drive() method might be a method for moving the car around the screen.

Constructor

The constructor is the initialisation function of a class. This function is called when an a new instance (a new object) of a class is created.

An object is created with the command 'new' and the subsequent call to the constructor. 

Attribute

Attributes are the variables of a class.

Methods

Methods are the functions of a class.

Child classes - Keyword 'extends'

A The basic principle of a class can be derived from another class, keeping all the original's qualities and allowing us to make new ones. This new class inherits the methods and attributes of of the base class. However, if new methods or attributes in the child class have the same names as those in the base class, the base class properties are overwritten. To call the constructor of a base class (in the case of a child class), the keyword 'super' is used.

The structure of the child class:

class className extends basicClass
{

[Attributes - Variables]
[Constructor – Initialising function]

[Methods- Functions]

}

Example BallClass

Note, that this example file uses tabs and multiple files for the first time. These are just to help us organise our code. When we run our program p5.js access the classes and treats them as a part of the main code. As general rule, use a seperate file for each class, using the name of the class as the file name. understood and used fairly quickly, and in some regards it Object Oriented Coding lends itself to a more Intuitive understanding of code. However, there is a lot of nuance and theory to writing a good class and it takes considerable practice.

Example BallClass

Below the draw function, you will find the BouncingBall class. It’s common practice to separate classes into their own file, to help keep code organised.

var ball1;
var ball2;
 
var p1;
var p2;
var drag = false;
 
function setup()
{
  createCanvas(800,600);
  p1= createVector();
  p2= createVector();
  ball1 = new BouncingBall(100,100, 30);
  ball2 = new BouncingBall(50,50);
 
  imageMode(CENTER);
  smooth(, 10);
}
 
function draw()
{
  background(255);
  fill(255,255,255,60);
  rect(0,0,width,height);
 
  if(drag)
  { // draw the direction of shoot
    p1.set(ball1._pos.x,ball1._pos.y,0);
    line(p1.x,p1.y,p2.x,p2.y);
  }
 
  // draw the balls
  ball1.draw();
  ball2.draw();

}
 
function mousePressedmouseClicked() {
  drag = true;
  p1.set(ball1._pos.x,ball1._pos.y,0);
  p2.set	ball1.setDirection(mouseX, mouseY,0);
}  
function mouseDragged()
{
  p2.setball2.setDirection(mouseX,mouseY,0);
}
 
function mouseReleased()
{
  drag = false;
 
  // shooting direction calculation. 
  var dir = p5.Vector.sub(p2,p1);
  // shorten the length 
  dir.mult(0.09);
 
  //the ball is given a new direction 
  ball1.set(p1,dir,0.993);
  ball2.set(p2,dir,0.95 mouseY);
}

Example BouncingBall

class BouncingBall
{
   // constructor 
  constructor(shapeWidth, shapeHeightx,y,radius)
  {
    this._posx = createVector(width/2, height/2)x;
    this._diry = createVector(0,0)y;
		this.velocityX = 1;
 		this._dampVvelocityY = 1;
     
    this._wdampV = shapeWidth0.99;
    		this._hgravity = shapeHeight1.9;

    
    this._shaper = loadImage("ball.png")radius;
  }
   
  // set the new position + direction + dampening
  setsetDirection(postargetX,dir,dampVtargetY)
  {
		let newVelocityX =  targetX-this._pos = pos;
 x
		let newVelocityY = targetY-this.y
  	this._dir.add(dir)velocityX =  newVelocityX *0.10;
    	this._dampVvelocityY = dampV newVelocityY*0.10;
  }
   
  // update the current position
  calcPos()
  {
		
		// add gravity 
		this.velocityY += this.gravity;
		
    // curentapply positionfriction shiftedto velocity
   this._pos.add(velocityX =  this.velocityX * this._dir)dampV;
  this.velocityY =  this.velocityY * this._dampV;
		  
		// add movementvelocity vectorto modifiedposition
    this._dir.mult(x += this._dampV)velocityX;
    this.y += this.velocityY;
		
    // test horisontal 
    if(this._pos.x + this._w/2r > width)
    {
      this._dir.xvelocityX *= -1;
      this._pos.x = width - this._w/2r;
    }
    else if(this._pos.x - this._w/2r < 0)
    {
      this._dir.xvelocityX *= -1;
      this._pos.x = this._w/2r;
    }
     
    // test vertical 
    if(this._pos.y + this._h/2r > height)
    {
      this._dir.yvelocityY *= -1;
      this._pos.y = height - this._w/2r;
    }
    else if(this._pos.y - this._h/2r < 0)
    {
      this._dir.yvelocityY *= -1;
      this._pos.y = this._h/2r;
    }

    
  }
   
  // draw the ball
  draw()
  {
    this.calcPos();
    imagecircle(this._shape,this._pos.x,this._pos.y,this._w,this._hr);
  }
}

Link to full exercise

Exercise A

• Modify the program , so that several many new balls can be placed independently of each other.

Exercise B

• Extend the class again to make a third kind of ball. Modify its attributes and methods to create new kinds of behavior.

• are placed on the screen. Using an array and a for loop, it’s possible to quickly add hundreds balls!

Polymorphism

...

Object-Oriented Coding (using classes to organise code) provides a number of powerful ways to use classes and objects. One more advanced feature is inheritance, where a class can be based on an existing class. This new class inherits the methods and attributes of the base class. However, if new methods or attributes in the child class have the same names as those in the base class, the base class properties are overwritten. To reference the constructor of a base class from a child class, the keyword 'super' is used.

The structure of the child class:

class className extends basicClass
{

[Attributes - Variables]
[Constructor – Initialising function]

[Methods- Functions]

}

Example BallClass Extended 

class BallEx extends BouncingBall
{
  constructor(size)
  {
     super(size,size);
  }
 
  function draw()
  {
    super.draw();
    line(0, 0 , this._pos.x,this._pos.y);
  }
 
}