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Trying to create a gravity system but keep getting NullPointerException and can't find the error...

[7 Replies]
- 09-Jul-2013 03:59 PM
- Forum: Programming Questions
Hey,

Can anyone help me understand why I'm getting a NullPointerException?

I'm new to this and from what I understand it means I didn't initialize something.. I just can't seem to find what..

I'm trying to learn create a gravitational system, here is my code:

float G_CONSTANT = 6.674;

Planet moon,earth;

void setup(){

size(500,500);

moon = new Planet(100,100,10);

earth = new Planet(300,300,30);

}

void draw(){

moon.display();

moon.gravitationPull(earth);

earth.display();

earth.gravitationPull(moon);

}

class Planet {



int x,y;

float radius = 0;

float mass;

PVector location, velocity, acceleration,gravitation;





Planet(int x_, int y_, float radius_){



x = x_;

y = y_;



location = new PVector(x,y);

velocity = new PVector(0,0);

acceleration = new PVector(0,0);

mass = PI * sq(radius);



}



void display() {



noStroke();

fill(0);

ellipse(x,y,radius*2,radius*2);



}



void gravitationPull(Planet planet_) {

PVector dist = PVector.sub(planet_.location,this.location);

float GmDividedbyMag= ((-G_CONSTANT*planet_.mass)/dist.mag());

PVector gravitation = PVector.mult(dist,GmDividedbyMag);

acceleration = planet_.gravitation;

acceleration.div(planet_.mass);

velocity.add(acceleration);

location.add(velocity);



}





}

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