function ProductsCollection()
{
	this.collection = new Array();
	this.iSize = 0;
}

ProductsCollection.prototype.getInstance = function()
{
	if ( !ProductsCollection.prototype.instance )
		ProductsCollection.prototype.instance = new ProductsCollection();
	return ProductsCollection.prototype.instance;
}

ProductsCollection.prototype.put = function( product )
{
	this.collection[ product.sId ] = product;
}

ProductsCollection.prototype.collect = function()
{
	var iQuantityTotal = 0;
	var iPriceTotal = 0;
	for ( sId in this.collection )
	{
		var product = this.collection[ sId ];
		if ( product.iQuantity > 0 )
		{ // input present
			iQuantityTotal += product.iQuantity;
			iPriceTotal += product.iPrice * product.iQuantity;
		}
	}
	return new Product( "", iPriceTotal, iQuantityTotal );
}