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Command Pattern

Command Pattern

Enclose your request under an object as a command and pass it to the object which can invoke the appropriate behavior by using appropriate object which will handle the passed command and execute it.

Its an Action

Advantage 

  • It separates the invoker and the executor based on command operation.
    • for example an invoker will invoke the relevant object for command execution.
  • New command can be easily added.
It command pattern, have 4 actors.
  1. Command Request : Encapsulates command and its parameters.
  2. Receiver : who knows how to perform the requested action.
  3. Invoker : Sends the command request
  4. Client : create and configure the command and the invoker.

Usage
  • When parametrized object is required as per required action
  • creation and execution of request at different times
  • when logging , transaction, rollback is required
  • Its often used in a scenarios where you want to decouple the sender (client) of the request from the receiver (the object that performs the action) and provide a level of abstraction for invoking action

There are following participant in command design pattern

Command : an Interface for executing an operation.
ConcreteCommand : It extends the Command interface to execute the method. This class creates the binding between the action and the receiver.
Invoker : This class asks the command to carry out the request
Receiver : This class knows the operation.

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