Why Functional Programming Matter

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 instructions that mimic the low-level vocabulary of a computer (for example, assignment, conditional branching, and loops).

- Declarative programming: you give rules saying what you want, and you expect the system to decide how to achieve it.

Functional programming = side-effect-free + declarative programming

Functional programming exemplifies the idea of declarative programming ("just say what you want, using expressions that don't interact, and for which the system can choose the implementation") and side-effect-free which is mentioned above when using immutable objects approach.

Reference

Image result for java 8 in action

Alan Mycroft and Mario Fusco, Java 8 in Action: Lambdas, Streams, and Functional-style Programming. Part 4. Beyond Java 8.

Comments

[Snippet] CSS - Child element overlap parent

I searched from somewhere and found that a lot of people says a basic concept for implementing this feature looks like below: HTML code: <div id="parent"> <div id="child"> </div> </div> And, CSS: #parent{ position: relative; overflow:hidden; } #child{ position: absolute; top: -1; right: -1px; } However, I had a lot of grand-parents in my case and the above code didn't work. Therefore, I needed an alternative. I presumed that my app uses Boostrap and AngularJs, maybe some CSS from them affects mine. I didn't know exactly the problem, but I believed when all CSS is loaded into my browser, I could completely handle it. www.tom-collinson.com I tried to create an example to investigated this problem by Fiddle . Accidentally, I just changed: position: parent; to position: static; for one of parents -> the problem is solved. Look at my code: <div class="modal-body dn-placeholder-parent-positi...

BIRT - Fix the size of an image

I use a dynamic image as a logo my report in pdf. At the beginning, I use table to align the logo in left or right. I meet a problem with some images with a large width or height. My customer requires that the logo should be displayed in original size. These following steps solves my problem: 1. Use Grid instead of Table 2. Set Grid "Height" is 100% and "Width" is blank 3. Set "Fit to container" for images are "true". Download the the template here .

JSF 2 - Dynamically manipulating the component tree with system events

Let's suppose we want to modify the metadata (attributes) of elements such as render , requried , maxlength but we do not define in JSF tags. The manipulating components can be conducted in Drools files, for example. How could we do? I think that is what we need to change something of component tree during JSF life-cycle. JSF supports event handling throughout the JSF life-cycle. In this post, I use two events: postAddToView for scanning components tree and preRenderView for manipulating the meta of components before rendering to GUI. I modified my own project from previous post for this example. This is my first further JSF trying out with the project as I said before. :) We define the tags f:event below the form - a container component of the components which we want to work on. The valid values for the attribute type for f:event can be found from tag library document of JSF 2. <!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml" x...

The HelloWorld example of JSF 2.2 with Myfaces

I just did by myself create a very simple app "HelloWorld" of JSF 2.2 with a concrete implementation Myfaces that we can use it later on for our further JSF trying out. I attached the source code link at the end part. Just follow these steps below: 1. Create a Maven project in Eclipse (Kepler) with a simple Java web application archetype "maven-archetype-webapp". Maven should be the best choice for managing the dependencies , so far. JSF is a web framework that is the reason why I chose the mentioned archetype for my example. 2. Import dependencies for JSF implementation - Myfaces (v2.2.10) into file pom.xml . The following code that is easy to find from http://mvnrepository.com/ with key words "myfaces". <dependency> <groupId>org.apache.myfaces.core</groupId> <artifactId>myfaces-api</artifactId> <version>2.2.10</version> </dependency> <dependency> <groupId>org.apache.myfaces.core<...

Tip for resolving the compile errors when importing a Maven project in Eclipse

Sometimes, I import a existing Maven project into Eclipse and I get some compile errors related to "pom.xml", "facet version of Web", and so on. It was really frustrating me because I even cleaned, built and updated the project many times but the errors still occurred. I accidentally found the following steps to resolve this issue but honestly I still don't know why. Step 1 : Delete the project that met the compile errors in Eclipse, but don't delete it on disk. Step 2 : Open the project (by Windows Explorer if you use Windows) and remove file/folder ".classpath", ".settings" and ".project" . Step 3 : Import the project back into Eclipse. ---^0^--- Maven is a build automation tool used primarily for Java projects. Eclipse is an integrated development environment (IDE).

vhandit

Search This Blog