Balistic curve

public class Balistics {
    static double t=0.;
    static double dt=0.002;
    static double m=0.01;
    static double alpha = 0.001;
    static vector r=new vector();
    static vector v= new vector(10.*Math.cos(Math.PI/4.),0.,10.*Math.sin(Math.PI/4.));
    static vector g = new vector(0.,0.,-9.81);
    static vector a = new vector();
    static vector f=new vector();

    public static vector R(vector v){//poloha
        r.x=RComponent(r.x, v.x, dt);
        r.y=RComponent(r.y, v.y, dt);
        r.z=RComponent(r.z, v.z, dt);
        return r;
    }

    public static vector F(vector v){//sila odporu
        f.x=FComponent(v.x, v.abs());
        f.y=FComponent(v.y, v.abs());
        f.z=FComponent(v.z, v.abs());
        return f;
    }

    public static vector A(vector f){//zrychlenie
        a.x=AComponent(f.x, m) + g.x;
        a.y=AComponent(f.y, m) + g.y;
        a.z=AComponent(f.z, m) + g.z;
        return a;
    }

    public static vector V(vector a){//rychlost
        v.x=VComponent(v.x, a.x, dt);
        v.y=VComponent(v.y, a.y, dt);
        v.z=VComponent(v.z, a.z, dt);
        return v;
    }

    private static double FComponent(double vComponent, double absv){
        return (-alpha*absv*vComponent);
    }

    private static double AComponent(double fComponent, double m){
        return (fComponent/m);
    }

    private static double RComponent(double rComponent, double vComponent, double dt){
        return (rComponent + vComponent*dt);
    }

    private static double VComponent(double vComponent, double aComponent, double dt){
        return (vComponent + aComponent*dt);
    }

    public static void makestep(){//krok v case o dt
        r=R(v);
        f=F(v);
        a=A(f);
        v=V(a);
        t=t+dt;
    }

    public static void main(String[] args) {
        for (int i = 0; i<1000;i++){
            makestep();
            System.out.println("time: "+t+" x: "+r.x+" z:"+r.z+" a.x: "+a.x+" a.z: "+a.z+" v.x: "+v.x+" v.z: "+v.z+" f.x: "+f.x+" f.z: "+f.z);
        }
    }

}
class vector{
    public double x,y,z;
    vector(){
        x=0;y=0;z=0;
    }
    vector(double x, double y, double z){
        this.x=x; this.y=y; this.z=z;
    }
    public void add(vector r){
        x=x+r.x; y=y+r.y; z=z+r.z;
    }
    public vector Add(vector r){
        vector tmp=new vector(this.x+r.x,this.y+r.y,this.z+r.z);
        return tmp;
    }

    public double abs(){
        return Math.sqrt(this.x*this.x+this.y*this.y+this.z*this.z);
    }
    public vector Mult(double alpha){
        vector tmp = new vector(alpha*this.x, alpha*this.y,alpha*this.z);
        return tmp;
    }

    public double scalarprod(vector r){
        return(x*r.x+y*r.y+z*r.z);
    }
}