The command design pattern is a behavioral design pattern that involves four players, as in the following example:

• Client
• Invoker
• Command 
• Receiver

In very simple words, the receiver is the object on screen such as a textbox and button and the command is sendKeys and click. We encapsulate the command in an object and pass it to the receiver.

The actual command design pattern also supports an Undo operation, but we will not consider the Undo operation here. By using command objects, it becomes easier to build generic components that need to assign, delegate, or execute method calls without needing to know the class of the method or the method parameters. Using an invoker object allows command executions to be conveniently performed. Using this, we can also create different modes for commands that are handled by the invoker object without the client needing to be aware of the existence of the different modes involved.

The main players in a command design pattern are the Client, the invoker, the command, and the receiver. Let's understands all four from a framework perspective.