Welcome!

Java IoT Authors: Yeshim Deniz, Pat Romanski, Elizabeth White, Liz McMillan, Zakia Bouachraoui

Related Topics: Java IoT

Java IoT: Article

Inversion of Control Rocks

Inversion of Control Rocks

Inversion of Control (IoC) is about software components doing what they are told, when they are told. Your OO application could well become unmaintainable without it.

IoC is a pattern that helps teams avoid the dependency hell that results when an application grows into a large pseudo-platform without taking care to adequately decouple logic; that thing that ultimately only a couple of its omnipotent architects or old-lag premium-rate contractors really understand; that system that Heath Robinson and Rube Goldberg might have made together (look them up).

The problem with small working applications that become large is that static-method entanglement does not scale. One part of a system that's otherwise fairly self-contained statically accesses another part of the system and cannot be instantiated without invoking methods in the latter. Thus it can't easily be isolated for unit testing. What's more, it can't be developed as an independent component. Components that are developed separately can have their own development teams and may well be part of a larger design. These components will have their own source control directory and can be developed against mock implementations of their dependent components. All this will help overall development become faster, in terms of both the team's efficiency and the build time.

As an example, let's take a Personal Information Manager (PIM) application that has UI and persistence elements. The naïve implementation might have inline JDBC statements among graphical code. A componentized application would have that persistence logic separated into a persistence component with user interface logic enshrined in a view-controller component. Clearly, if the two teams developing their respective components agree on a slowly evolving interface/implementation-separated API for persistence, they can develop at their own pace and ship versions of their components whenever it's appropriate.

A third piece, which is not a component, would be the bootstrap for the application. That bootstrap may well be entirely contained in a static main method of a simple class and would merely instantiate the two components, passing one into the other's constructor before invoking setVisible(true) or similar. With the introduction of this bootstrap we can see the control aspect of the IoC pattern.

In a noncomponentized version of our example, the view-controller may well have its own main method, might instantiate a fixed version of the PIM store, or access it via an unnecessary singleton factory (public static methods are generally bad), i.e., the control is very much inside the component in question.

The word "inversion" from the pattern name is about getting control back. The containing application (often a true container or a proper framework rather than a main method) controls when a component is instantiated and which implementations of its dependent components it is passed.

IoC also dictates the configuration of components. A JDBC version of the PIM store above would clearly require some JDBC settings. Classically, developers may write a mechanism to retrieve them from a fixed properties file. IoC would insist that the configuration is passed into the component. In our hypothetical example, it would take it via the constructor and be interface/implementation separated. Thus the configuration is a component. It would be tightly coupled to the component that requires it, but subject to multiple implementations, one of which may be the "from properties file".

Inversion of Control has moved to the center stage in the last six months after a five-year gestation period. There are three types of Inversion of Control. Type 1 uses configuration data (Avalon, JContainer); Type 2 uses bean introspection (Spring Framework, WebWork2, HiveMind); Type 3 uses constructor signatures (PicoContainer).

For a componentized system that uses singletons or similar for component resolution, the dependency is obscure. In IoC it is declarative. The application would have loosely coupled components and be more scalable, more maintainable, and more testable. It's a very small investment for a very large return. Inversion of Control rocks.

More Stories By Paul Hammant

Paul Hammant is a still-coding architect for ThoughtWorks in London and has been programming professionally since 1989. He was a former committer on Apache’s Avalon project, but left and cofounded the open-source PicoContainer project and its sister NanoContainer as well as remaining involved the post-Avalon JContainer project.

Comments (4)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


IoT & Smart Cities Stories
Machine learning has taken residence at our cities' cores and now we can finally have "smart cities." Cities are a collection of buildings made to provide the structure and safety necessary for people to function, create and survive. Buildings are a pool of ever-changing performance data from large automated systems such as heating and cooling to the people that live and work within them. Through machine learning, buildings can optimize performance, reduce costs, and improve occupant comfort by ...
René Bostic is the Technical VP of the IBM Cloud Unit in North America. Enjoying her career with IBM during the modern millennial technological era, she is an expert in cloud computing, DevOps and emerging cloud technologies such as Blockchain. Her strengths and core competencies include a proven record of accomplishments in consensus building at all levels to assess, plan, and implement enterprise and cloud computing solutions. René is a member of the Society of Women Engineers (SWE) and a m...
Poor data quality and analytics drive down business value. In fact, Gartner estimated that the average financial impact of poor data quality on organizations is $9.7 million per year. But bad data is much more than a cost center. By eroding trust in information, analytics and the business decisions based on these, it is a serious impediment to digital transformation.
DXWorldEXPO LLC announced today that Ed Featherston has been named the "Tech Chair" of "FinTechEXPO - New York Blockchain Event" of CloudEXPO's 10-Year Anniversary Event which will take place on November 12-13, 2018 in New York City. CloudEXPO | DXWorldEXPO New York will present keynotes, general sessions, and more than 20 blockchain sessions by leading FinTech experts.
Apps and devices shouldn't stop working when there's limited or no network connectivity. Learn how to bring data stored in a cloud database to the edge of the network (and back again) whenever an Internet connection is available. In his session at 17th Cloud Expo, Ben Perlmutter, a Sales Engineer with IBM Cloudant, demonstrated techniques for replicating cloud databases with devices in order to build offline-first mobile or Internet of Things (IoT) apps that can provide a better, faster user e...
Bill Schmarzo, Tech Chair of "Big Data | Analytics" of upcoming CloudEXPO | DXWorldEXPO New York (November 12-13, 2018, New York City) today announced the outline and schedule of the track. "The track has been designed in experience/degree order," said Schmarzo. "So, that folks who attend the entire track can leave the conference with some of the skills necessary to get their work done when they get back to their offices. It actually ties back to some work that I'm doing at the University of ...
Charles Araujo is an industry analyst, internationally recognized authority on the Digital Enterprise and author of The Quantum Age of IT: Why Everything You Know About IT is About to Change. As Principal Analyst with Intellyx, he writes, speaks and advises organizations on how to navigate through this time of disruption. He is also the founder of The Institute for Digital Transformation and a sought after keynote speaker. He has been a regular contributor to both InformationWeek and CIO Insight...
Rodrigo Coutinho is part of OutSystems' founders' team and currently the Head of Product Design. He provides a cross-functional role where he supports Product Management in defining the positioning and direction of the Agile Platform, while at the same time promoting model-based development and new techniques to deliver applications in the cloud.
Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settlement products to hedge funds and investment banks. After, he co-founded a revenue cycle management company where he learned about Bitcoin and eventually Ethereal. Andrew's role at ConsenSys Enterprise is a mul...
In his session at 21st Cloud Expo, Raju Shreewastava, founder of Big Data Trunk, provided a fun and simple way to introduce Machine Leaning to anyone and everyone. He solved a machine learning problem and demonstrated an easy way to be able to do machine learning without even coding. Raju Shreewastava is the founder of Big Data Trunk (www.BigDataTrunk.com), a Big Data Training and consulting firm with offices in the United States. He previously led the data warehouse/business intelligence and Bi...