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You're a developer. What do you do in your spare time? One of my most excited task for sharpening my skills is starting build a pet project. Motivation Slack is cool! It's free. It supports for team collaboration very well. However, my team only has storage limits due to a free account. We got a warning message as below: Your file was uploaded — it’s safe and sound in Slack. Unfortunately your team doesn’t have any storage space left. To get more space, you can upgrade to a paid account or delete some of your older files. Since my team plan of upgrading to a paid account is still up in the air, I intended to go with "deleting some of our older files" first. (But we will, Slack. You are great!) Play Around I got started by googling keyword "remove slack files". Here it is: https://get.slack.help/hc/en-us/articles/218159688-Delete-shared-files Uh huh! But I only could delete one file at a time . We're afraid it's not possible t

Today, I was just curious about why an enum can not extend anything else. I took a look on the Oracle document here , and I found the answer is below: "All enums implicitly extend java.lang.Enum. Because a class can only extend one parent (see Declaring Classes), the Java language does not support multiple inheritance of state (see Multiple Inheritance of State, Implementation, and Type), and therefore an enum cannot extend anything else." I have been learned of it before. But, wait a sec...! Why Java does not support multiple inheritance of state? Since I have worked with other programming languages like C++, I was able to make a class extend some other classes. The short answer is to avoid the issues of multiple inheritance of state .  I wonder if other programming languages have these below terms but Java does. Multiple inheritance of state It is the ability to inherit fields from multiple classes. There is a problem and Java avoids it. "For exa

"A good DSL minimizes the 'communication gap' between a domain concept and the code that implements it" - Robert C. Martin A Use Case It looks like adopting a new technology is always driven by a business need. The organizations, such as banks, have their own business processes (such as data gathering and document management). These processes are different from others but usually the differences are not big. How do we build a product which can be reused the similar features but still be adaptable with the specific requirements of each bank? Then, the answer is we should have a library/framework. There is an idea that we can implement this library/framework by using a business rules engine. Which has the following benefits: Be able to modify implementation of business domain at runtime (such as XML, CSV) S ource code is more readable for both developers and domain experts. Therefore, source code can be consider it as a document Since Business Rules Engine

So far, the Template Method has been my most used design pattern. That is the reason why this post is quite long. J Definition from Wiki The Template Method defines the program skeleton of an algorithm in a method, deferring some steps to subclasses. It lets one redefine certain steps of an algorithm without changing the algorithm's structure. A Real World Use Case Imagine that you have many different kinds of documents. You want to generate a pdf file from a corresponding word template. Each type has its own small modifications but the main process for document generating is the same. We apply the Template Method for this case. We define a final method including some steps (such as preparing for content, generating file) at a superclass. There are three possibilities for these steps at subclasses: Must be overridden: abstract methods. Not mandatory to be overridden: default protected methods. Can not be overridden: default private methods. Dissecting the Patt

Everyone talks about it, but not everyone knows what it is. Why DevOps? In general, whenever an organization adopts any new technology, methodology, or approach, that adoption has to be driven by a business need. Any kind of system that need rapid delivery of innovation requires DevOps (development and operations). Why? DevOps requires mechanisms to get fast feedback from all the stakeholders in the software application that's being delivered. DevOps approaches to reduce waste and rework and to shift resources to higher-value activities. DevOps aims to deliver value (of organization or project) faster and more efficiently. DevOps Capabilities The capabilities that make up DevOps are a broad set that span the software delivery life cycle. The following picture is a reference architecture which provides a template of a proven solution by using a set of preferred methods and capabilities. My Remarks Okay, that sounds cool. What does it simply mean, again? The f

WOW! How meaningful this below video explains about the name of  "I/O". Sundar Pichai talked a lot of Machine Learning Machine Learning is a very hot trend these days. Google uses it for their products. Google Assistant: Easily booking an online meal by talking with Google Assistant like a staff of partners, for example. Google Home: Hands-free calling. Google Photos: sharing suggestion, shared library, photo books and google lens. Youtube: 360 degree video, live stream. Kotlin became an official programming language for Android https://kotlinlang.org I'm on the way to Kotlin! ^^ Reference: [1]. https://www.youtube.com/watch?v=Y2VF8tmLFHw

What issues do we concern when implementing and maintaining systems? One of the most concern is debugging during maintenance: "this code crashed because it observed some unexpected value." Then, it turns out that the ideas of  no side effects  and  immutability , which functional programming promotes, can help. Shared mutable data is the root cause Shared mutable data are read and updated by more than one of the methods. Share mutable data structures make it harder to track changes in different parts of your program. An immutable object is an object that can't change its state after it's instantiated so it can't be affected by the actions of a function. It would be a dream to maintain because we wouldn't have any bad surprises about some object somewhere that unexpectedly modifies a data structure. A new thinking: Declarative programming There are two ways thinking about implementing a system by writing a program. - Imperative programming: has