import processing. pdf.*;
                
ArrayList history = new ArrayList();
                
float distthresh = 60;
                


                
void setup(){
                
  size(900,600);
                
  background(255);
                
  stroke(0,50);
                
  smooth();
                
}
                


                


                
void draw(){
                
  
                
}
                


                
void mouseDragged(){
                


                
  PVector d = new PVector(mouseX,mouseY,0);
                
  history.add(0,d);
                
  
                
  for (int p=0; p<history.size(); p++){
                
    PVector v = (PVector) history.get(p);
                
    float joinchance = p/history.size() + d.dist(v)/distthresh;
                
    if (joinchance < random(0.4))  line(d.x,d.y,v.x,v.y);
                
  }
                
}
                


                
void keyPressed(){
                
  if (key == ' ') {
                
    background(255);
                
    history.clear();
                
  }
                
}
               

Then I get errors when I type in the rest of the code below when I run the file. It does not export.

void setup() {
  size(400, 400, PDF, "filename.pdf");
}

void draw() {
  // Draw something good here
  line(0, 0, width/2, height);

  // Exit the program 
  println("Finished.");
  exit();
}