Welcome!

Java IoT Authors: Yeshim Deniz, Elizabeth White, Pat Romanski, Liz McMillan, Chris Schwarz

Related Topics: Java IoT

Java IoT: Article

Three Sources of a Solid Object-Oriented Design

Design heuristics, scientifically proven OO design guidelines, and the world beyond the beginning

Object-oriented design is like an alloy consisting of a solid grounding in the object-oriented (OO) approach and implementing the best OO practices heavily laced with how to sidestep the OO pitfalls. The design process isn't only a matter of applying basic OO principles. One should go further and achieve a reasonable tradeoff between OO design principles and applicable design patterns. This article will discuss the relationship between three sources of a solid OO design and offer a starting point to understanding what is, in effect, a complex process. It will also serve as a review for experienced designers.

The OO Design Pyramid

When developers first turn to object-oriented development, they try to grasp the basics. It may take several project lifetimes. Getting a full sense of object orientation is a big shift in people's minds, especially for those who come from the procedural world. Such principles are like ABC books since they define the foundation of the OO world.

Once people get a sense of the basic principles, they start feeling the power of the OO approach. In our experience this is a dramatic moment for every OO designer and developer. The euphoria of possessing a powerful methodology can make them feel completely self-sufficient and they stop and don't try for perfection. It takes time to realize that there are significant issues beyond the basics that can be found in the accumulated wisdom of the OO developer community and are expressed in a set of design heuristics and scientifically proven OO design guidelines. Some OO designers jump to using design patterns everywhere like a cookie recipe. Although design patterns are important and useful tools in building OO systems, they're just templates that define a common design language and significantly improve design quality, when properly used.

To build contemporary real-world enterprise-class systems, OO designers should (a) be proficient in basic OO principles, (b) master the principles of OO design, and (c) understand design patterns. Otherwise the chance of design flaws and total cost of system ownership increases. And, with growing adoption of Service Oriented Architecture (SOA), the robustness of the SOA services can depend directly on the solidity of the OO design of underlying components.

The pyramid in Figure 1 represents three sources of a solid OO design. It also defines a systematic view of design and uncovers dependencies between these sources.

Now let's discuss each level of this pyramid from an architectural and design point of view. Of course there's no way to explain these topics completely in such short article, but we'll try to highlight the necessity of paying attention to the dependencies and their impact on the quality of OO design.

Basic OO principles

The first level of the OO design pyramid is formed by a set of basic OO principles.

The most basic OO principles include encapsulation, inheritance, and polymorphism. Along with abstraction, association, aggregation, and composition, they form the foundation of the OO approach. These basic principles rest on a concept of objects that depicts real-world entities such as, say, books, customers, invoices, or birds. These classes can be considered templates for object instantiation, or object types. In other words, class specifies what an object can do (behavior) and defines patterns for its data (state). Modeling the real world in terms of an object's state and behavior is the goal of the OO approach. In this case, state is represented by a set of object attributes, or data, and behavior is represented by the object's methods.

Now we'll discuss the application of basic OO principles to modeling.

Encapsulation encloses data and behavior in a programming module. Encapsulation is represented by the two close principles of information hiding and implementation hiding. Information hiding restricts access to the object data using a clearly defined "interface" that hides the internal details of the object's structure. For each restricted class variable, this interface appears as a pair of "get" and "set" methods that define read-and-write access to the variable. Implementation hiding defines the access restrictions to the object methods also using a clearly defined interface that hides the internal details of object implementation and exposes only the methods that comprise object behavior. Both information and implementation hiding serve the main goal - assuring the highest level of decoupling between classes.

Inheritance is a relationship that defines one entity in terms of another. It designates the ability to create new classes (types) that contain all the methods and properties of another class plus additional methods and properties. Inheritance combines interface inheritance and implementation inheritance. In this case, interface inheritance describes a new interface in terms of one or more existing interfaces, while implementation inheritance defines a new implementation in terms of one or more existing implementations. Both interface inheritance and implementation inheritance are used to extend the behavior of a base entity.

Polymorphism is the ability of different objects to respond differently to the same message. Polymorphism lets a client make the same request of different objects and assume that the operation will be appropriate to each class of object. There are two kinds of polymorphism - inheritance polymorphism, which works on an inheritance chain, and operational polymorphism, which specifies similar operations for non-related out-of-inheritance classes or interfaces. Because inheritance polymorphism lets a subclass (subtype) override the operation that it inherits from its superclass (supertype), it creates a way to diversify the behavior of inherited objects in an inheritance chain, while keeping their parent-objects intact. Polymorphism is closely related to inheritance as well as to encapsulation.

Naturally, some OO principles are controversial in the sense that they contradict one another. For example, to be able to inherit from a class, one should know the internal structure of that class, while encapsulation's goal is exactly the opposite - it tries to hide as much of the class structure as possible. In real life the tradeoff between these two principles is a fine line that can't be established without stepping up to the next level in the design pyramid.

OO Design Principles and Heuristics

OO design principles and heuristics form the second level in OO design pyramid.

There are about a dozen OO design principles and four dozens OO design heuristics identified over the years by OO evangelists such as Grady Booch, Bertrand Meyer, Robert C. Martin, Barbara Liskov, and others. OO design principles define the most common scientifically derived approaches for building robust and flexible systems. These approaches proved to be the best tools in solving numerous OO design issues that can't be captured by fundamental OO principles.

The class structure and relationships group consists of the following design principles: the Single Responsibility Principle (SRP), the Open/Closed Principle (OCP), the Liskov Substitution Principle (LSP), the Dependency Inversion Principle (DIP), and the Interface Segregation Principle (ISP).

The Single Responsibility Principle specifies that class should have only one reason to change. It's also known as the cohesion principle and dictates that class should have only one responsibility, i.e., it should avoid putting together responsibilities that change for different reasons.

The Open/Closed Principle dictates that software entities should be open to extension but closed to modification. Modules should be written so that they can be extended without being modified. In other words, developers should be able to change what the modules do without changing the modules' source code.

The Liskov Substitution Principle says that subclasses should be able to substitute for their base classes, meaning that clients that use references to base classes must be able to use the objects of derived classes without knowing them. This principle is essentially a generalization of a "design by contract" approach that specifies that a polymorphic method of a subclass can only replace its pre-condition by a weaker one and its post-condition by a stronger one.

Dependency Inversion Principle says high-level modules shouldn't depend on low-level modules. In other words, abstractions shouldn't depend on details. Details should depend on abstractions.

The Interface Segregation Principle says that clients shouldn't depend on the methods they don't use. It means multiple client-specific interfaces are better than one general-purpose interface.

More Stories By Gene Shadrin

Gene Shadrin is an enterprise architect with 17 years of software development experience, including object-oriented analysis, design, architecture, and development of real-life enterprise Java systems. He is a Sun Certified Enterprise Architect, PMP, and consults government and Fortune 500 organizations. Gene can be contacted at [email protected]

PUBLICATIONS
------------
Third Annual International Conference of Open systems. Moscow, Russia 1996. Thesis of lecture
Client-Server Technology Journal. Russia, 1996, 3-4 (double). ?PowerBuilder - Open Tool for Client-Server Computing? article.
Database Management Systems Journal. Russia, 1996, 5-6 (double). ?PowerBuilder - Open Tool for Complex Distributed Client-Server Computing? article.
?PowerBuilder: Developer?s Guide? Book. Translation from English. Russia, 1997, MIR Publishing-house (400 pages)
Database Management Systems Journal. Russia, 1997, 5-6 (double). "PFC Basics" article

Comments (0)

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.


@ThingsExpo Stories
"We are focused on SAP running in the clouds, to make this super easy because we believe in the tremendous value of those powerful worlds - SAP and the cloud," explained Frank Stienhans, CTO of Ocean9, Inc., in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
While the focus and objectives of IoT initiatives are many and diverse, they all share a few common attributes, and one of those is the network. Commonly, that network includes the Internet, over which there isn't any real control for performance and availability. Or is there? The current state of the art for Big Data analytics, as applied to network telemetry, offers new opportunities for improving and assuring operational integrity. In his session at @ThingsExpo, Jim Frey, Vice President of S...
The financial services market is one of the most data-driven industries in the world, yet it’s bogged down by legacy CPU technologies that simply can’t keep up with the task of querying and visualizing billions of records. In his session at 20th Cloud Expo, Karthik Lalithraj, a Principal Solutions Architect at Kinetica, discussed how the advent of advanced in-database analytics on the GPU makes it possible to run sophisticated data science workloads on the same database that is housing the rich...
Internet of @ThingsExpo, taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 21st Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devic...
"The Striim platform is a full end-to-end streaming integration and analytics platform that is middleware that covers a lot of different use cases," explained Steve Wilkes, Founder and CTO at Striim, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
SYS-CON Events announced today that Calligo, an innovative cloud service provider offering mid-sized companies the highest levels of data privacy and security, has been named "Bronze Sponsor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Calligo offers unparalleled application performance guarantees, commercial flexibility and a personalised support service from its globally located cloud plat...
SYS-CON Events announced today that DXWorldExpo has been named “Global Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Digital Transformation is the key issue driving the global enterprise IT business. Digital Transformation is most prominent among Global 2000 enterprises and government institutions.
SYS-CON Events announced today that Datera, that offers a radically new data management architecture, has been named "Exhibitor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Datera is transforming the traditional datacenter model through modern cloud simplicity. The technology industry is at another major inflection point. The rise of mobile, the Internet of Things, data storage and Big...
"We provide IoT solutions. We provide the most compatible solutions for many applications. Our solutions are industry agnostic and also protocol agnostic," explained Richard Han, Head of Sales and Marketing and Engineering at Systena America, in this SYS-CON.tv interview at @ThingsExpo, held June 6-8, 2017, at the Javits Center in New York City, NY.
"We've been engaging with a lot of customers including Panasonic, we've been involved with Cisco and now we're working with the U.S. government - the Department of Homeland Security," explained Peter Jung, Chief Product Officer at Pulzze Systems, in this SYS-CON.tv interview at @ThingsExpo, held June 6-8, 2017, at the Javits Center in New York City, NY.
DX World EXPO, LLC., a Lighthouse Point, Florida-based startup trade show producer and the creator of "DXWorldEXPO® - Digital Transformation Conference & Expo" has announced its executive management team. The team is headed by Levent Selamoglu, who has been named CEO. "Now is the time for a truly global DX event, to bring together the leading minds from the technology world in a conversation about Digital Transformation," he said in making the announcement.
"MobiDev is a Ukraine-based software development company. We do mobile development, and we're specialists in that. But we do full stack software development for entrepreneurs, for emerging companies, and for enterprise ventures," explained Alan Winters, U.S. Head of Business Development at MobiDev, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
SYS-CON Events announced today that DXWorldExpo has been named “Global Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Digital Transformation is the key issue driving the global enterprise IT business. Digital Transformation is most prominent among Global 2000 enterprises and government institutions.
In his opening keynote at 20th Cloud Expo, Michael Maximilien, Research Scientist, Architect, and Engineer at IBM, discussed the full potential of the cloud and social data requires artificial intelligence. By mixing Cloud Foundry and the rich set of Watson services, IBM's Bluemix is the best cloud operating system for enterprises today, providing rapid development and deployment of applications that can take advantage of the rich catalog of Watson services to help drive insights from the vast t...
SYS-CON Events announced today that EnterpriseTech has been named “Media Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. EnterpriseTech is a professional resource for news and intelligence covering the migration of high-end technologies into the enterprise and business-IT industry, with a special focus on high-tech solutions in new product development, workload management, increased effic...
SYS-CON Events announced today that Massive Networks, that helps your business operate seamlessly with fast, reliable, and secure internet and network solutions, has been named "Exhibitor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. As a premier telecommunications provider, Massive Networks is headquartered out of Louisville, Colorado. With years of experience under their belt, their team of...
SYS-CON Events announced today that Cloud Academy named "Bronze Sponsor" of 21st International Cloud Expo which will take place October 31 - November 2, 2017 at the Santa Clara Convention Center in Santa Clara, CA. Cloud Academy is the industry’s most innovative, vendor-neutral cloud technology training platform. Cloud Academy provides continuous learning solutions for individuals and enterprise teams for Amazon Web Services, Microsoft Azure, Google Cloud Platform, and the most popular cloud com...
SYS-CON Events announced today that Cloudistics, an on-premises cloud computing company, has been named “Bronze Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Cloudistics delivers a complete public cloud experience with composable on-premises infrastructures to medium and large enterprises. Its software-defined technology natively converges network, storage, compute, virtualization, and ...
SYS-CON Events announced today that CHEETAH Training & Innovation will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct. 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. CHEETAH Training & Innovation is a cloud consulting and IT training firm specializing in improving clients cloud strategies and infrastructures for medium to large companies.
SYS-CON Events announced today that Datanami has been named “Media Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Datanami is a communication channel dedicated to providing insight, analysis and up-to-the-minute information about emerging trends and solutions in Big Data. The publication sheds light on all cutting-edge technologies including networking, storage and applications, and thei...