Behavioral Patterns : Command

Properties:

-          Encapsulates  set of actions to achive a task.

-          A command can be executed to complete a task without need to know what it does.

Implementation:

-          A Command interface declares method or methods that encapsulates actions.

-          A Receiver is passed to a command object and does the actual work that is specific to certain task.

-          Concrete Command class defines actual steps to achieve a certain task.

-          Invoker invokes the commands objects.

-          Client creates command objects and passes to invoker for execution.

Java Standard Library Implementations:

-          java.lang.Runnable

-          javax.swing.Action

Example Usage:

class ConcreteCommand extends Runnable{

    Reveiver _receiver;

    public ConcreteCommand(Reveiver _receiver){

        this._receiver=receiver;

    }

   

    public void run(){

        _reveiver.doAction();

        System.out.println("Action is completed!")

        _receiver.cleanUp();

    }

}

public static void main(String[] args){

    // invoker is responsible for executing the commands

    ExecutorService executerService = new ThreadPoolExecutor(

        5, 5, TimeUnit.MINUTES,new ArrayBlockingQueue<Runnable>(5, true));

   

    //receiver does the actual work

    Receiver receiver = new Receiver();

   

    // Command object is created with receiver object passed to it

    Runnable command = new ConcreteCommand(receiver);

   

    // command is invoked

    executerService.execute(command);

    executerService.shutdown();

}