[F9] Vector class help

[Fall_X]

Hi,

Never been any good with vectors, but I decided to give it a shot and write a vector class, as part of a simple physics engine. But since I'm no good at it, I'm not sure if it's, well, any good. Could someone please have a look and see if the calculations look right, and if there's anything I could/should have done differently? Thanks.

package com.gamesquid.physicsquid {
    // Written by Sven Magnus
    public class Vector {
        // public variables
        // use these in favour of the getters for slightly better performance
        // however, don't set them directly unless you know what you're doing
        public var _x1:Number=0;
        public var _y1:Number=0;
        public var _x2:Number=0;
        public var _y2:Number=0;
        public var _vx:Number=0;
        public var _vy:Number=0;
        public var _length:Number=0;
        public var _angle:Number=0;
        // getter functions
        public function get x1():Number {
            return this._x1;
        }
        public function get y1():Number {
            return this._y1;
        }
        public function get x2():Number {
            return this._x2;
        }
        public function get y2():Number {
            return this._y2;
        }
        public function get vx():Number {
            return this._vx;
        }
        public function get vy():Number {
            return this._vy;
        }
        public function get length():Number {
            return this._length;
        }
        public function get angle():Number {
            return this._angle;
        }
        public function get degrees():Number {
            return this._angle*180/Math.PI;
        }
        public function get dx():Number {
            return this._vx/this._length;
        }
        public function get dy():Number {
            return this._vy/this._length;
        }
        public function get rx():Number {
            return -this._vy;
        }
        public function get ry():Number {
            return this._vx;
        }
        public function get lx():Number {
            return this._vy;
        }
        public function get ly():Number {
            return -this._vx;
        }
        public function get normal():Vector {
            return new Vector(this._x1,this._y1,this.dx,this.dy);
        }
        public function get right():Vector {
            return new Vector(this._x1,this._y1,this.rx,this.ry);
        }
        public function get left():Vector {
            return new Vector(this._x1,this._y1,this.lx,this.ly);
        }
        // setter functions
        public function set x1(value:Number):void {
            this._x1=value;
            this._vx=this._x2-value;
            this._length=Math.sqrt(this._vx*this._vx+this._vy*this._vy);
            this._angle=Math.atan2(this._vy,this._vx);
        }
        public function set y1(value:Number):void {
            this._y1=value;
            this._vy=this._y2-value;
            this._length=Math.sqrt(this._vx*this._vx+this._vy*this._vy);
            this._angle=Math.atan2(this._vy,this._vx);
        }
        public function set x2(value:Number):void {
            this._x2=value;
            this._vx=value-this._x1;
            this._length=Math.sqrt(this._vx*this._vx+this._vy*this._vy);
            this._angle=Math.atan2(this._vy,this._vx);
        }
        public function set y2(value:Number):void {
            this._y2=value;
            this._vy=value-this._y1;
            this._length=Math.sqrt(this._vx*this._vx+this._vy*this._vy);
            this._angle=Math.atan2(this._vy,this._vx);
        }
        public function set vx(value:Number):void {
            this._vx=value;
            this._x2=this._x1+value;
            this._length=Math.sqrt(this._vx*this._vx+this._vy*this._vy);
            this._angle=Math.atan2(this._vy,this._vx);
        }
        public function set vy(value:Number):void {
            this._vy=value;
            this._y2=this._y1+value;
            this._length=Math.sqrt(this._vx*this._vx+this._vy*this._vy);
            this._angle=Math.atan2(this._vy,this._vx);
        }
        public function set angle(value:Number):void {
            this._angle=value;
            this._vx=this._length*Math.cos(value);
            this._vy=this._length*Math.sin(value);
            this._x2=this.x1+this._vx;
            this._y2=this.y1+this._vy;
        }
        public function set length(value:Number):void {
            this._length=value;
            this._vx=value*Math.cos(this._angle);
            this._vy=value*Math.sin(this._angle);
            this._x2=this.x1+this._vx;
            this._y2=this.y1+this._vy;
        }
        // constructor
        public function Vector(x1:Number,y1:Number,vx:Number,vy:Number):void {
            this._x1=x1;
            this._y1=y1;
            this._vx=vx;
            this._vy=vy;
            this._x2=this._x1+this._vx;
            this._y2=this._y1+this._vy;
            this._length=Math.sqrt(this._vx*this._vx+this._vy*this._vy);
            this._angle=Math.atan2(this._vy,this._vx);
        }
        // public functions
        public function add(v:Vector):Vector {
            return new Vector(this._x1,this._y1,this._vx+v._vx,this._vy+v._vy);
        }
        public function substract(v:Vector):Vector {
            return new Vector(this._x1,this._y1,this._vx-v._vx,this._vy-v._vy);
        }
        public function dotProduct(v:Vector):Number {
            return this._vx*v._vx+this._vy*v._vy;
        }
        public function project(v:Vector):Vector {
            var dp:Number=this._vx*v._vx+this._vy*v._vy;
            return new Vector(this._x1,this._y1,dp*this.dx,dp*this.dy);
            return new Vector(this._x1,this._y1,dp*this.dx,dp*this.dy);
        }
    }
} 

EDIT: I realize there's some redundancy in there, some stuff that gets repeated that could have been put in functions - like the calculation of the dotproduct when projecting vectors, or recalculating the angle and length - but I figured it would be a tiny bit faster like this, and it's not like these calculations will ever change, right? Unless I made a mistake with them, that is.