public class Particle extends Point3D {

   public Point3D v;
   public double mass;
   public int color;
   public int intensity;
   public int opacity;
   
   public Particle() { }
   
   public Particle(double x, double y, double z) {
     super(x, y, z);
   }
   
   public Particle(double x, double y, double z, double dx, double dy, double dz) {
     super(x, y, z);
     this.v = new Point3D(dx, dy, dz);
   }
   
   public void advance(double t, Point3D acc) {
     v.x += acc.x*t;
     v.y += acc.y*t;
     v.z += acc.z*t;
     x += v.x*t;
     y += v.y*t;
     z += v.z*t;
   }
   
   public void advanceAcc(double t, double ddx, double ddy, double ddz) {
     v.x += ddx*t;
     v.y += ddy*t;
     v.z += ddz*t;
     x += v.x*t;
     y += v.y*t;
     z += v.z*t;
   }
   
   public void simpleAdvance(double t, double dx, double dy, double dz) {
     x += dx*t;
     y += dy*t;
     z += dz*t;
   }
   
   public String toString() {
     return getClass().getName()+"[ ("+x+" , "+y+" , "+z+") v=("+v.x+" , "+v.y+" , "+v.z+") ]";
   }
   
}