deutsche Version

Classes are one of the most important programming constructs of Java and many other programming languages. They are the abstract model or blueprint for an object. 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 as  methods, but otherwise they work pretty much the same to as the variables and functions we already know. But in In order to get access to these attributes and methods we need to user use a dot syntax: a , 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 

The constructor is the initialisation function of a class. This function is called when an 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. 

...

The structure of the child class:

class className extends basicClass
{

[Attributes - Variables]
[Constructor – Initialising function]

[Methods- Functions]

}

Example

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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 , processing puts these all together p5.js access the classes and treats them as one long documenta 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. 

BouncingBallvar ball1;
BouncingBallvar ball2;
 
PVector      p1 = new PVector();
PVector      p2 = new PVector();
boolean      var p1;
var p2;
var drag = false;
 
voidfunction setup()
{
  sizecreateCanvas(800,600);
  p1= createVector();
  p2= createVector();
  ball1 = new BouncingBall(100,100);
  ball2 = new BouncingBall(50,50);
 
  shapeModeimageMode(CENTER);
  smooth();
}
 
voidfunction 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();

}
 
voidfunction mousePressed()
{
  drag = true;
  p1.set(ball1._pos.x,ball1._pos.y,0);
  p2.set(mouseX,mouseY,0);
}
 
voidfunction mouseDragged()
{
  p2.set(mouseX,mouseY,0);
}
 
voidfunction mouseReleased()
{
  drag = false;
 
  // shooting direction calculation. 
  PVectorvar dir = PVectorp5.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(p1p2,dir,0.95);
}

BouncingBall

class BouncingBall
{
  PVector _pos;

 PVector
_dir;   float   _dampV;
  PShape  _shape;
  int     _w;
  int     _h;
   
  // constructor 
  BouncingBallconstructor(int shapeWidth,int shapeHeight)
  {
    this._pos = new PVectorcreateVector(width/2, height/2);
    this._dir = new PVectorcreateVector(0,0);
    this._dampV = 1;
     
    this._w = shapeWidth;
    this._h = shapeHeight;
     
    this._shape = loadShapeloadImage("ball1ball.svgpng");
  }
   
  // set the new position + direction + dampening
  void set(PVector pos,PVector dir,float dampV)
  {
    this._pos = pos.get();
    this._dir.add(dir);
    this._dampV = dampV;
  }
   
  // update the current position
  void calcPos()
  {
    // curent position shifted
    this._pos.add(this._dir);
     
    // movement vector modified
    this._dir.mult(this._dampV);
     
    // test horisontal 
    if(this._pos.x + this._w/2 > width)
    {
      this._dir.x *= -1;
      this._pos.x = width - this._w/2;
    }
    else if(this._pos.x - this._w/2 < 0)
    {
      this._dir.x *= -1;
      this._pos.x = this._w/2;
    }
     
    // test vertical 
    if(this._pos.y + this._h/2 > height)
    {
      this._dir.y *= -1;
      this._pos.y = height - this._w/2;
    }
    else if(this._pos.y - this._h/2 < 0)
    {
      this._dir.y *= -1;
      this._pos.y = this._h/2;
    }
     
  }
   
  // draw the ball
  void draw()
  {
    this.calcPos();
     shapeimage(this._shape,
          this._pos.x,this._pos.y,
          this._w,this._h);
  }
}
 

Download Example

Image Removed

Link to full exercise

Exercise 12 A

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

Exercise 12 B

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

Example BallKlasse BallClass Extended 

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