Welcome!

Java IoT Authors: Elizabeth White, Yeshim Deniz, Pat Romanski, 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
Dion Hinchcliffe is an internationally recognized digital expert, bestselling book author, frequent keynote speaker, analyst, futurist, and transformation expert based in Washington, DC. He is currently Chief Strategy Officer at the industry-leading digital strategy and online community solutions firm, 7Summits.
Digital Transformation is much more than a buzzword. The radical shift to digital mechanisms for almost every process is evident across all industries and verticals. This is often especially true in financial services, where the legacy environment is many times unable to keep up with the rapidly shifting demands of the consumer. The constant pressure to provide complete, omnichannel delivery of customer-facing solutions to meet both regulatory and customer demands is putting enormous pressure on...
IoT is rapidly becoming mainstream as more and more investments are made into the platforms and technology. As this movement continues to expand and gain momentum it creates a massive wall of noise that can be difficult to sift through. Unfortunately, this inevitably makes IoT less approachable for people to get started with and can hamper efforts to integrate this key technology into your own portfolio. There are so many connected products already in place today with many hundreds more on the h...
The standardization of container runtimes and images has sparked the creation of an almost overwhelming number of new open source projects that build on and otherwise work with these specifications. Of course, there's Kubernetes, which orchestrates and manages collections of containers. It was one of the first and best-known examples of projects that make containers truly useful for production use. However, more recently, the container ecosystem has truly exploded. A service mesh like Istio addr...
Digital Transformation: Preparing Cloud & IoT Security for the Age of Artificial Intelligence. As automation and artificial intelligence (AI) power solution development and delivery, many businesses need to build backend cloud capabilities. Well-poised organizations, marketing smart devices with AI and BlockChain capabilities prepare to refine compliance and regulatory capabilities in 2018. Volumes of health, financial, technical and privacy data, along with tightening compliance requirements by...
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...
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...
To Really Work for Enterprises, MultiCloud Adoption Requires Far Better and Inclusive Cloud Monitoring and Cost Management … But How? Overwhelmingly, even as enterprises have adopted cloud computing and are expanding to multi-cloud computing, IT leaders remain concerned about how to monitor, manage and control costs across hybrid and multi-cloud deployments. It’s clear that traditional IT monitoring and management approaches, designed after all for on-premises data centers, are falling short in ...
In his general session at 19th Cloud Expo, Manish Dixit, VP of Product and Engineering at Dice, discussed how Dice leverages data insights and tools to help both tech professionals and recruiters better understand how skills relate to each other and which skills are in high demand using interactive visualizations and salary indicator tools to maximize earning potential. Manish Dixit is VP of Product and Engineering at Dice. As the leader of the Product, Engineering and Data Sciences team at D...
Dynatrace is an application performance management software company with products for the information technology departments and digital business owners of medium and large businesses. Building the Future of Monitoring with Artificial Intelligence. Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more busine...