Implementing the Command pattern in the real world
We will take up an example of the stock exchange (much talked about in the Internet world) to demonstrate the implementation of the Command pattern. What happens in a stock exchange? You, as a user of the stock exchange, create orders to buy or sell stocks. Typically, you don't buy or sell them; it's the agent or broker who plays the intermediary between you and the stock exchange. The agent is responsible for taking your request to the stock exchange and getting the work done. Imagine that you want to sell a stock on Monday morning when the exchange opens up. You can still make the request to sell stock on Sunday night to your agent even though the exchange is not yet open. The agent then queues this request to be executed on Monday morning when the exchange is open for the trading. This presents a classical case for the Command pattern.
Design considerations
Based on the UML diagram, you learned that the Command pattern has four main participants...
