Classes are one of the most important programming constructs of Java and many other 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 much the same to the variables and functions we already know. But in order to get access to these attributes and methods we need to user dot syntax: a "." must be placed after the object name, followed by the name of the attribute or the method.
...
| Code Block |
|---|
BouncingBall ball1;
BouncingBall ball2;
PVector p1 = new PVector();
PVector p2 = new PVector();
boolean drag = false;
void setup()
{
size(800,600);
ball1 = new BouncingBall(100,100);
ball2 = new BouncingBall(50,50);
// svg bild soll
zentriert sein
shapeMode(CENTER);
smooth();
}
void draw()
{
// hintergrund loeschen
//background(255);
//
ghosting fill(255,255,255,60);
rect(0,0,width,height);
if(drag)
{ // zeichne die abschussrichtungdraw the direction of shoot
p1.set(ball1._pos.x,ball1._pos.y,0);
line(p1.x,p1.y,p2.x,p2.y);
}
// zeichnedraw denthe ballballs
ball1.draw();
ball2.draw();
}
void mousePressed()
{
drag = true;
p1.set(ball1._pos.x,ball1._pos.y,0);
p2.set(mouseX,mouseY,0);
}
void mouseDragged()
{
p2.set(mouseX,mouseY,0);
}
void mouseReleased()
{
drag = false;
// shooting abschussdirection staerkecalculation. berechnen
PVector dir = PVector.sub(p2,p1);
// shorten the laengelength verkuerzen
dir.mult(.09);
// der ball wird neu ausgerichtetthe ball is given a new direction
ball1.set(p1,dir,.993);
ball2.set(p1,dir,.95);
}
|
...
| Code Block |
|---|
class BouncingBall
{
PVector _pos;
PVector _dir;
float _dampV;
PShape _shape;
int _w;
int _h;
// constructor
BouncingBall(int shapeWidth,int shapeHeight)
{
_pos = new PVector(width/2, height/2);
_dir = new PVector(0,0);
_dampV = 1;
_w = shapeWidth;
_h = shapeHeight;
_shape = loadShape("ball1.svg");
}
// set the new position + direction + dampening
void set(PVector pos,PVector dir,float dampV)
{
_pos = pos.get();
_dir.add(dir);
_dampV = dampV;
}
// update the current position
void calcPos()
{
// curent position shifted
_pos.add(_dir);
// movement vector modified
_dir.mult(_dampV);
// test horisontal
if(_pos.x + _w/2 > width)
{
_dir.x *= -1;
_pos.x = width - _w/2;
}
else if(_pos.x - _w/2 < 0)
{
_dir.x *= -1;
_pos.x = _w/2;
}
// test vertical
if(_pos.y + _h/2 > height)
{
_dir.y *= -1;
_pos.y = height - _w/2;
}
else if(_pos.y - _h/2 < 0)
{
_dir.y *= -1;
_pos.y = _h/2;
}
}
// draw the ball
void draw()
{
calcPos();
shape(_shape,
_pos.x,_pos.y,
_w,_h);
}
}
|
Download Example
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 Extended
| Code Block |
|---|
class BallEx extends BouncingBall
{
BallEx(int size)
{
super(size,size);
}
void draw()
{
super.draw();
line(0,0,_pos.x,_pos.y);
}
}
|
Download Example
Exercise:
...