NullPointerException and couldn't initialize sketch errors in Processing

Question

I wrote a physical simulation about gravitational force between two planets.It worked perfectly fine so I decided to take it to a new level and rewrote it using arrays and five planets(circles).But my code gives strange and never the same error. I get either NullPointerException error or the VM error when intializing the sketch(No description just the "Vm error couldn't initialize skecth" and the "see help and troubleshoot" bullsh*t) The program uses a txt file to read in data(double-checked and it works fine). My Array names and descriptions are

PVector - Pos stands for Position
PVector - Vel stands for Velocity
PVector - Acc stands for Acceleration
PVector - Dist stands for Distance
PVector - Dir stands for Direction
float - Mass stands for Mass

My code:

 public PVector[] Pos = new PVector[5];
public PVector[] Acc = new PVector[5];
public PVector[] Vel = new PVector[5];
public PVector[] Dist = new PVector[5];
public PVector[] Dir = new PVector[5];
public float[] Mass = new float[5];
void setup(){
 String Data[] = loadStrings("Data.txt");
 size(800,800);
 for(int g = 0;g < 5;g++){
   Pos[g] = new PVector(float(Data[g+1]),float(Data[g+6]));
   Vel[g] = new PVector(float(Data[g+12]),float(Data[g+17]));
   Mass[g] = float(Data[g+23]);
 }
}
void draw(){
 for (int i = 0;i < 5;i++){
   for (int f = 0;f < 5;f++){
     if(i !=f){
       if(Pos[i].x < Pos[f].x){Dir[f].x = 1;Dist[f].x = (Pos[f].x - Pos[i].x);}else{ // I get the error here
       if(Pos[i].x > Pos[f].x){Dir[f].x = -1;Dist[f].x = (Pos[i].x - Pos[f].x);}else{
       if(Pos[i].x == Pos[f].x){Dir[f].x = 0;Dist[f].x = 0;}}}
       if(Pos[i].y < Pos[f].y){Dir[f].y = 1;Dist[f].y = (Pos[f].y - Pos[i].y);}else{
       if(Pos[i].y > Pos[f].y){Dir[f].y = -1;Dist[f].y = (Pos[i].y - Pos[f].y);}else{
       if(Pos[i].y == Pos[f].y){Dir[f].y = 0;Dist[f].y = 0;}}}
       if ((Dist[f].x != 0)){
         Acc[i].x+=((6*((Mass[i]*Mass[f])/Dist[f].magSq())/10000000)/Mass[i])*Dir[f].x;// *6/1000000 is MY G constant
       }
       if ((Dist[f].y != 0)){
         Acc[i].y+=((6*((Mass[i]*Mass[f])/Dist[f].magSq())/10000000)/Mass[i])*Dir[f].y;
       }
     }
   }
   Vel[i].x = Vel[i].x + Acc[i].x;
   Vel[i].y = Vel[i].y + Acc[i].y;
   Pos[i].x = Pos[i].x + Vel[i].x;
   Pos[i].y = Pos[i].y + Vel[i].y;
   ellipse(Pos[i].x,Pos[i].y,10,10);
 }
}

Ok my Data.txt contains:"Pos: 10 60 110 160 210 10 60 110 160 210 Vel: 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Mass: 1 1 1 1 1" All spaces are new lines! I hope I gave all the information needed to help me out. — user4676310
on which line you get NullPointerException? Why you dont insert stack trace of these errors? — libik
@libik The code has coments in it concerning where do i get the error — user4676310
@Sipi you got your answer already kind of but I still say your code is not indented and so not readable at all. — Kick Buttowski

libik libik · Accepted Answer · 2015-03-23T18:26:25

You create array of PVectors of size 5 here : public PVector[] Dir = new PVector[5]; . In this moment, it has null five times for indexes 0-4 in it.

Because you do not create new PVectors in this array, when you try to access variable x in here Dir[f].x, you got error, because Dir[f] is null and you cant access variable x of null -> NullPointerException.

In this part you are instantizing some arrays

for(int g = 0;g < 5;g++){
   Pos[g] = new PVector(float(Data[g+1]),float(Data[g+6]));
   Vel[g] = new PVector(float(Data[g+12]),float(Data[g+17]));
   Mass[g] = float(Data[g+23]);
 }

You should add instantizing also for Dir, Acc and Dist

Note also, that you are working with objects, not with primitive data types. null is not same as new PVector(0,0)

Also from "design" point of view, using arrays this way is NOT good approach. You should create your own class Planet, where each planet holds information about its properties and in your main class you handle interaction between them.

How to create "empty" or "zero" variables instead of nulls? Just create them :)

for(int g = 0;g < 5;g++){
   Pos[g] = new PVector(float(Data[g+1]),float(Data[g+6]));
   Vel[g] = new PVector(float(Data[g+12]),float(Data[g+17]));
   Mass[g] = float(Data[g+23]);
   Dir[g] = new PVector(0,0);
   Acc[g] = new PVector(0,0);
   Dist[g] = new PVector(0,0);
 }

PS : I do not how exactly is this class implemented, using new PVector() or new PVector(0) instead of new PVector(0,0) may also work.

NullPointerException and couldn't initialize sketch errors in Processing

1 Answers