ActionScript 3 External Classes

package {

	import flash.display.MovieClip;
	import flash.geom.ColorTransform;
	import flash.events.*;

	/*
	This class represents the Star movie clip we drew on the stage.
	We extend this class to a movie clip, thus allowing us to use movie
	clip's functions and properties.
	*/
	public class Star extends MovieClip {

		private var starColor:uint;
		private var starRotation:Number;

		/*
		This is called the constructer of the class.
		It is called every time we create a new Star instance.
		In the constructor, we assign a random color to the star and set some
		of it's properties.
		*/
		public function Star () {

			//Calculate a random color
			this.starColor = Math.random() * 0xffffff;

			// Get access to the ColorTransform instance associated with star.
			var colorInfo:ColorTransform = this.transform.colorTransform;

			// Set the color of the ColorTransform object.
			colorInfo.color = this.starColor;

			// apply the color to the star
			this.transform.colorTransform = colorInfo;

			//Assign a random alpha for the star
			this.alpha = Math.random();

			//Assign a random rotation speed
			this.starRotation =  Math.random() * 10 - 5;

			//Assign a random scale
			this.scaleX = Math.random();
			this.scaleY = this.scaleX;

			//Add ENTER_FRAME where we do the animation
			addEventListener(Event.ENTER_FRAME, rotateStar);
		}

		//This function is responsible for the rotation of the star
		private function rotateStar(e:Event):void {
			this.rotation += this.starRotation;
		}
	}
}

/*
Create 100 stars on the stage.
Assign a random position to each.
All the star animation etc. are done in the "Star" class.
*/
for (var i = 0; i < 100; i++) {
	var star:Star = new Star();
	star.x = stage.stageWidth * Math.random();
	star.y = stage.stageHeight * Math.random();
	addChild (star);
}