/* * Spring.java *  * Created on 26/10/2007 *  * To change this template, choose Tools | Templates * and open the template in the editor. */package demos.nehe.lesson40;/** * Java implementation of Erkin Tunca's "Spring" class from "Physics2.h" by Scott Rains.<br/> * Date: 26 Oct 2007 * * @author Scott Rains (sid.rains[at]gmail.com) */public class Spring {    Mass mass1;                                // The First Mass At One Tip Of The Spring    Mass mass2;                                // The Second Mass At The Other Tip Of The Spring    float springConstant;                            // A Constant To Represent The Stiffness Of The Spring    float springLength;                            // The Length That The spring Does Not Exert Any Force    float frictionConstant;                            // A Constant To be Used For The Inner Friction Of The Spring    public Spring(Mass mass1, Mass mass2, float springConstant, float springLength, float frictionConstant) {        this.springConstant = springConstant;                // Set The springConstant        this.springLength = springLength;                // Set The springLength        this.frictionConstant = frictionConstant;            // Set The frictionConstant        this.mass1 = mass1;                        // Set mass1        this.mass2 = mass2;                        // Set mass2    }    public void solve() {                            // solve() Method: The Method Where Forces Can Be Applied        Vector3D springVector = mass1.pos.subtract(mass2.pos);        // Vector Between The Two Masses        float r = springVector.length();                // Distance Between The Two Masses        Vector3D force = new Vector3D();                // Force Initially Has A Zero Value        if (r != 0) {                            // To Avoid A Division By Zero... Check If r Is Zero            // The Spring Force Is Added To The Force            Vector3D temp = springVector.divide(r).multiply((r - springLength) * (-springConstant));            force.addTo(temp);        }        Vector3D fictionForce = mass1.vel.subtract(mass2.vel);        fictionForce.multiplyTo(-frictionConstant);        force.addTo(fictionForce);                                      // The Friction Force Is Added To The force        // With This Addition We Obtain The Net Force Of The Spring        mass1.applyForce(force);                    // Force Is Applied To mass1        mass2.applyForce(force.negative());                // The Opposite Of Force Is Applied To mass2    }                                    // Void Solve() Ends Here}