//Use the Observer Pattern.
//The Runner class creates the IBM Stock object, two Investors and attach them as observers to the Stock object.
// Fluctuating prices of IBM Stock will notify Investors.
IBM ibm = new IBM("IBM", 120.00);
ibm.Attach(new Investor("Investor 1"));
ibm.Attach(new Investor("Investor 2"));

ibm.Price = 120.10;
ibm.Price = 121.00;
ibm.Price = 120.50;
ibm.Price = 120.75;