Code:

class Particle
{
  float x, y;
  float speedx, speedy;
  float speed;
  float mass;
  color c;
  Particle(float tempx, float tempy, float tempspeed, float tempmass)
  {
    x = tempx;
    y = tempy;
    speed = tempspeed;
    mass = tempmass;
    c = color(random(225), random(225), random(225));
  }
  void display()
  {
    fill(c);
    noStroke();
    ellipse(x, y, mass, mass);
  }
  void move()
  {
    speedx = speedx+((random(1)-0.5)*speed);
    speedy = speedy+((random(1)-0.5)*speed);
    x = x + speedx;
    y = y + speedy;
  }
}
Particle[] particles;
void setup()
{
  size(200, 200);
  particles = new Particle[0];
}
void draw()
{
  background(0);
  particles = append(particles, new Particle(mouseX, mouseY, 1, 20));
  for(int i = 0; i < particles.length; i++)
  {
    particles[i].display();
    particles[i].move();
  }
} 

I'm getting an error with the line that uses the append function.
What am I doing wrong here? The error I'm getting:
Code:

Cannot convert from Object to sketch_dec11a.Particle[] 

It doesn't matter whether I use append or splice.
I want to make an array of objects that gets bigger every frame, so that I can access the functions in them that make them move and display. If there's a more efficient way to do all this, I'd appreciate knowing it.