Problem with trails

Hi everyone, I am new at Processing. The question is that I have a homework and I have been given some code and asked to finished by creating a ball wich leaves a trail while moving. I have been trying for days without success. I will be really glad if someone can help me. It is supposed that from two classes I have to call a fucntion in the main program. I will leave here the code that I have been given. I hope someone can help me!! Thanks in advance!!

----------main program (dont trust in what is inside, it have been the result os my attempts)-------------------------

float x;
float y;
Trail trail = new Trail();
Trails trails = new Trails();
PVector startPoint;



void setup() {

  size(500, 500);

  for (int i = 0; i < trail.trailSize; i++) {  
     trails.Trails();
  }
}

void draw() {
  background(255);
  ellipse(x, y, 50, 50);



  if (mousePressed) {

    for (int i = 0; i < trails.maxTrails; i++) {
      trails.drawTrails();
    }
    x = mouseX;
    y = mouseY;
  }
}

------------------first class-----------------------------------------

class Trail {
  final int DEAD = 0;
  final int ALIVE = 1;
  final int ZOMBIE = 2;

  ArrayList<PVector> aTrail;
  color trailColor;
  int state;
  int tnumber;

  int trailSize = 1000;
  int totalTrails = 0;

  Trail() {
    aTrail = new ArrayList<PVector>(trailSize);
    trailColor = #6F480D;
    state = DEAD;
    tnumber = totalTrails + 1;
    totalTrails++;
  }

  int getTrailNumber() {
    return tnumber;
  }

  void addPointTrail(PVector p) {
    if (aTrail.size() > trailSize)
      aTrail.remove(0);
    aTrail.add(p);
  }

  void setColorTrail(color c) {
    trailColor = c;
  }

  void drawTrail() {
    float shade;

    if (aTrail.size() > 1) {
      shade = 256.0 / aTrail.size();
      for (int i=0; i < aTrail.size ()-1; i++) {
        strokeWeight(10);
        stroke(trailColor, shade*(i+1) );
        line(aTrail.get(i).x, aTrail.get(i).y, aTrail.get(i+1).x, aTrail.get(i+1).y);
      }
    }
  }

  void reduceTrail() {
    aTrail.remove(0);
    if (aTrail.size() == 0) setDeadTrail();
  }

  void setAliveTrail() {
    state = ALIVE;
  }

  void setDeadTrail() {
    state = DEAD;
  }

  void setZombieTrail() {
    state = ZOMBIE;
  }

  boolean isZombie() {
    return state == ZOMBIE;
  }

  boolean isDead() {
    return state == DEAD;
  }
}

---------- and the other class given is -------------------------------

class Trails {
  int maxTrails = 1000;
  ArrayList<Trail> aTrails;

  Trails() {
    aTrails = new ArrayList<Trail>(maxTrails);
  }

  int newTrail(PVector startPoint, color c) {
    Trail t = new Trail();

    aTrails.add(t);
    t.setColorTrail(c);
    t.addPointTrail(startPoint);
    t.setAliveTrail();
    return t.getTrailNumber();
  }

  void drawTrails() {
    Trail t;
    for (int i = 0; i < aTrails.size (); i++) {
      t = aTrails.get(i);
      t.drawTrail();
      if (t.isZombie()) t.reduceTrail();
      if (t.isDead()) aTrails.remove(i);
    }
  }

  void setZombieTrail(int tn) {
    Trail t;
    int i = 0;
    boolean found = false;

    t = aTrails.get(0);
    while ( i < aTrails.size() || !found) {
      t = aTrails.get(i);
      found = (t.getTrailNumber() == tn);
      i++;
    }

    t.setZombieTrail();
  }
}