In today’s blog, I will be discussing about a design pattern called the Command Design Pattern.

What is a Command Design Pattern?

Command Design Pattern is a behavioral design pattern in which an object is used to represent and encapsulate all the information needed to perform an action or trigger and event at a later time.

How does it work?

The requests are wrapped as commands and passed to invoker object. The invoker object then looks for the appropriate object which can handle this command and gives the command to the corresponding object that will execute this command. The base class contains an execute() method that simply calls the action on the reciever.

A command class includes some of the following: an object, the method to be applied to the object, and the arguments to be passed when the method is applied.

Command Design Pattern allows you to store lists of code that is executed at a later time or many times. Client do not know what the encapsulated objects are, they just call the Command to run when execute is called.  An object called the Invoker transfers this command to another object called the receiver to execute the right code.

How to Implement the Command Pattern?

First of, you have to create an interface that acts as a command.  Command object knows about the receiver and invokes a method of the receiver.

Second, create your objects(client) that will serve as requests.  The client decides which receiver objects it assigns to the command objects, and which commands it assigns to the invoker.

Third, create concrete command classes(also known as the receiver) that implements the command interface which will do the actual work when the execute() method in command is called.

Lastly, create an invoker object to identify which object will execute which command based on the type of command.  The invoker object does not know anything about the concrete command, it only knows the command interface.

I selected this post because I wanted to learn more about different patterns that is not covered in class. This post shows you what the Command Pattern is and how it works. It also shows you the different steps and an example code on how to use the command design. The diagram above is from the post.

The Command Pattern seems to be very useful when you found yourself using code that looks like:

if (…..)

do();

else if(……)

do();

else if(……)

do();

else if

……..

I think Command pattern is very useful when you are creating an interface where objects are waiting to be executed, just like the menu interface.

https://www.tutorialspoint.com/design_pattern/command_pattern.htm

From the blog cs-wsu – Computer Science by csrenz and used with permission of the author. All other rights reserved by the author.

For this blog, I am choosing one from Uncle Bob’s website, the Clean Coder Blog. Almost all of Uncle Bob’s blog are set up like a conversation. Uncle Bob writes questions that the readers might ask, and also answer them for the readers. It is really fun to read his blogs, it is usually short, and might answer some of your questions and give you more insight on the topic that he is writes about.

In his blog called “A Little About Patterns”, Uncle Bob talked a little bit about Design Patterns. In this blog, there were a lot of questions about why we still use Design Patterns that were made from the 90’s. It was mainly about the Design Patterns by the GOF(Gang of Four) book that was made popular in 1995. In the blog, Uncle Bob asked if the “person” could name a design pattern. He then pointed out the book GOF. The person then replied ” But isn’t that kind of old now and outdated?”. Uncle Bob then responded with “Indeed there are many newer books on the topic, and some are quite good; but none are quite so impactful and insightful as the original.”

Throughout the blog, Uncle Bob was just proving that, even though the GOF book was written 20 years ago, it still stands as the best book. He noted that “The Design Patterns book is one of the most important books, if not THE most important book, written about software within the last 20 years. In fact, the fundamentals of software have changed very little in the last four decades.” This just tells us that, even though it might seem like these designs are old, they are still the fundamental of Design Patterns.

Uncle Bob then said that most of the idea of the newer frameworks are old. That they are just Design Patterns. Then he gave this “person” the meaning of a design pattern. “A Design Pattern is a named canonical form for a combination of software structures and procedures that have proven to be useful over the years.”

The blog introduces a couple of newer Design Patterns like Model-View-Controller(MVC) which is a software architectural pattern for implementing user interfaces on computers, and how you can just say this is dependency injection and everybody will understand it in a way.

I chose this blog because it talked about design patterns and how the fundamentals which we are learning in class even if they were written from 20 years ago, are still the very core of Design Patterns. I think that to learn the proper way of using Design Patterns, we should learn about its fundamentals first.

From the blog cs-wsu – Site Title by csrenz and used with permission of the author. All other rights reserved by the author.

In Episode 68 of the CodingBlocks podcast,  they talked about the latest book, Clean Architecture by Robert Martin (colloquially known as Uncle Bob).  In the podcast, they explained the benefits of a clean architecture and why it matters. They said that the benefits of a clean architecture is that it can minimize efforts when it comes to adding features to the program.  Their functionality is maximized and changes are easy. It can reduce the number of people needed to write the software and adding features. They also added that there is no difference in design and architecture when it comes to a program. That the architecture should be incorporated into the design as well.  Throughout the podcast, they keep using the analogy of the Turtle and the Hare. They quoted that in the book, Uncle Bob added that “the only way to go fast, is to go well”. I think that this is a really good quote. Often we are bounded by the due date or time. In the podcast,

Also, in the podcast, they also said that “coding is easy, but managing our code when new features are added is the real challenge”. They said that maintaining cleanliness is better than cleaning it after the problems are piled up. Michael also talked about how sometimes, they say that the developers are not working. Which isn’t really the case. The problem lies in the architecture of the product since it does not support the changes that the product manager or client wants. They also talked about how sometimes company X comes to the market first but company Y is more successful because they were able to add more features faster than company X.

They also tackled the problem of rewriting the code, which most of us think would be the solution to the architectural problems. They said that rewriting is not the answer. Most of the time, we would rewrite the program to fix the problem. You will feel good about yourself when rewriting it since you are doing it really fast. But still not thinking about how to solve the architectural problem of your program. They said that the quality of your products should be taken seriously. Since developers are constrained by time most of the time, they forget the risk that are involved by being “fast”. Sometimes unit tests are not done and the code is not reusable anymore.

I chose to listen to this podcast because I wanted to learn more about Software Architecture and what are the benefits of having a good architecture versus just having a code that works. I  actually questioned Dr. Wurst about this, having done his first assignment for us. I asked him why we needed a better architecture even if the amount of classes in the program looks like a cluster. After listening to this podcast, it finally makes sense to me now. A product that have a better architecture is easier to change or add programs. In the long run, a better structured program is better and would be easier to manage than a program that is done “fast but not well”.

From the blog cs-wsu – Site Title by csrenz and used with permission of the author. All other rights reserved by the author.

In this blog, Mohamed Elgendy talked about why do we use model and some of the different kinds of diagrams used in UML.  Mohamed started off by explaining what UML is. He said that “UML is a set of standardized (Unified) diagrams, just like construction has front elevation, electrical diagram, floor plan, etc., UML offers different views of the same system.”. Which basically means that  UML is just a blueprint. In software development, we use this blueprint to better communicate with other people rather than software developers  in a way that they could understand.

In the blog, Mohamed explained different type and use of each diagrams and which team members are responsible for creating the diagram.

Class Diagram describes the structure of a system by showing the system’s classes, their attributes and the relationships among these classes. It display what interacts but not what happens when they interact.  The Class Diagrams are created by the Architects or the Technical Leads.

Component Diagram  are composed of one or more classes or interfaces. It is used to depict how various components of a system show dependencies. The Component Diagrams are used during the technical design and is also created by the Architect or the Technical Leads.

Deploying Diagram shows the physical relationship among the software and the hardware components in the system. In many cases, the component and deployment diagrams are combined in a single diagram. This is also created by the Architect or the Technical Leads.

Package Diagram shows the group of classes called “package”. Similar classes are grouped together if they do the same thing. Sometimes developers choose to display individual classes inside the package for better clarification. The Package Diagrams are created by the Architect or the Deployment Specialists.

Statechart Diagram describes the behavior of a system where  it shows the possible states  an object can be. It is typically drawn for objects that typically have a lot of dynamic behavior.  Statechart Diagrams are created by the Architect.

Object Diagram depicts a complete or partial view of the system at a specific time. Object Diagrams are created by the Developer.

Sequence  Diagram displays the sequence of events between entities of the system to show the dynamic view of the system. It is executed line by line showing the time ordering of messages.

Activity Diagrams describe the sequencing of actions and system’s logic. The starting point of this diagram is indicated by a large black dot and uses arrows to point to the order of actions.  Activity Diagram is typically used for objects are more complex that you would like to present clearly.

I selected this particular blog since we are using UML in Software Construction, Development, and Architecture class. I was actually a bit confused about how we used the diagrams in class. I was thinking that diagrams are just one program like we did in class, but diagrams are actually made to connect with other diagrams to explain how they interact with each other. In this blog, Mohamed added which team members are responsible for each diagrams. After reading this blog it is clear to me now that there are different responsibilities and types of people in a team. I thought that a team would be composed of all software developers, but in reality, some modeling diagrams are done by other professionals.

From the blog cs-wsu – Site Title by csrenz and used with permission of the author. All other rights reserved by the author.