|By Puneet Sangal||
|September 7, 2004 12:00 AM EDT||
A design pattern is a solution to a recurring problem. Although using patterns this way is well known and has been around for a while, it was only when the GoF wrote their famous book, Design Patterns, on software design patterns, that patterns slowly but surely became an industry standard.
A design pattern is not just object-oriented design, but the communication between these objects. The GoF Creational patterns are a specific subset of these patterns that create objects for you, rather than creating them directly. Why would you want that? It provides cleaner development and easier maintenance for your applications. I'll cover five creation patterns here, and attempt to help you learn and implement them. It's important to not only understand their usage, but also know when to use these patterns. (A basic knowledge of interfaces and abstract classes is assumed as a prerequisite for this article.)
I'll provide at least one simple way to implement each pattern, and at least one scenario in which you might use it. Of course, a complete description is beyond the scope of this article. The other two categories for patterns, as defined by the GoF, are structural and behavioral. We won't discuss these categories here, but instead will keep our focus on creational patterns.
The Factory Pattern
This pattern returns an instance of one of several possible classes based on the data passed. This allows us to introduce new classes without modifying the code substantially. An immediate advantage here is that the instantiation of the class occurs inside the Factory class, which provides more flexibility in code maintenance and development than having to create an object directly in the client of this class.
An example of a Factory pattern is the home interface of an EJB that instantiates a bean based on the data passed to it. Here's another simple hypothetical example. We have a Web site where users are required to enter their phone numbers. To keep our example simple, the phone number can be entered in one of two formats, as shown in Table 1.
Our implementation of the phone classes would look like Listing 1. In this listing we have a base abstract class and two subclasses. Our base class is abstract because we want to enforce instantiation of a subclass only. It's also not necessary to define a constructor for our base class. We have a PhoneFactory class that decides which of the subclasses would be returned based on the argument that is passed to the factory. The returned object from our factory is one of the subclasses, depending on the data passed. Now all a client class needs to do is call the getPhoneNumber() method in the factory class with the phone number as its argument.
The Abstract Factory Pattern
An abstract factory is a factory object that returns one of several related factories. There can't be any simpler definition. This means that instead of returning one subclass, it returns an abstract class that can in turn return a family of its subclasses. Thus both composition and inheritance play equally important roles here. The benefit of using this pattern is that it isolates the concrete subclasses from the client. This pattern should be used when the system is required to be independent of how the components are organized.
We'll expand our future example of phone numbers. If we internationalize our Web page, we can have different phone number types for different countries (see Table 2).
The implementation of the classes is shown in Listing 2. We have more or less a similar structure as before, only a little more complex. Here we have a base abstract class and two subclasses. The subclasses implement the abstract methods of the base class that are capable of returning a PhoneNumber object. We have an InternationalPhoneNumberFactory class that decides which of the subclasses would be returned based on the arguments that are passed to the factory. As before, all a client class needs to do is call the getInternationalPhoneNumber() method in the InternationalPhoneFactory class with the phone number as its argument. The instantiation details and which subclass gets instantiated are hidden from the user. Once we have an international phone number object, we can still have phone numbers with or without spaces for both of the countries. We would call the "with" or "without spaces" method using our previous PhoneFactory class, if required.
The Singleton Pattern
This pattern is used when a class can have only one instance in a system. Think of a Web application when one application-level class is used to track a number of clients. Multiple classes per session are unnecessary; just one for all the clients would suffice. This pattern can be achieved in a number of ways. For example, we can create an exception that will be thrown by a class if it's instantiated more than once. Next we'll have a boolean static variable in our class, because a static variable can be shared among all instances of a class. In the constructor of this class, we'll set this variable the first time it's instantiated. Any other time, since it is already set, the constructor would throw an exception if this variable is already set. This is an excellent strategy. But take care to de-set this variable when the instance is destroyed (in the finalize method). Different JVMs can exhibit different behaviors; using this would ensure we can instantiate an object of this class again after it is destroyed.
If a generic class is needed that only provides static methods, that class can also be declared as final. Using this final-static combination would prohibit any instance creation and allow us to use this class as a whole. Note that this is different from the earlier approach, where we actually created a single object of the class.
Another popular approach to creating Singleton patterns involves having a private constructor and a static method in a class. The private constructor would ensure that an instance can be created only from within the method of the class, which is static. The static method would return an instance and set a boolean variable indicating instance creation. As before, we would de-set this variable in the finalize method as a good coding practice.
These approaches are simple and direct, so I won't provide any example code for them.
The Builder Pattern
The Builder pattern allows a client object to construct a complex object by specifying its type and content only. The way in which objects are assembled can be achieved using a Factory pattern. The factory class used here is called Director, and the actual classes derived are called Builders. This pattern is similar to the abstract factory pattern because both return a family of objects. The difference, however, is that the abstract factory returns a family of related objects while the Builder pattern constructs a complex object one step at a time depending on the data supplied.
I'll attempt to describe a simpler example in which a Builder pattern can be used without providing a Java template for it, as that is beyond the scope of this article (constructing a Builder pattern, Java example would consume 150-200 lines of code). Consider a fast-food restaurant like Burger King where they have a special meal for kids. Irrespective of whether the order is chicken, a hamburger, or something else, the meal always consists of food and a toy. Here the client is the customer, the cashier is the director, and the restaurant crew is the builder. The builder knows how to build the meal, the director knows what to build, but they don't know how to perform each other's tasks. This is a layer of insulation the pattern provides us, that each can be varied without affecting the other.
The Prototype Pattern
This pattern is used when you want to copy an existing instance of a class, instead of creating a new one. Why? Because there might be so much data already in the object that it will take a considerable amount of time to get it again with a new instance. We can use the clone() method of the Object class to create a copy. Of course, the objects that can be cloned need to implement the Cloneable interface.
Imagine a list of value objects that can be obtained from a database that will contain a thousand objects. Each of these value objects would have a lot of information. This data is displayed on a particular Web page and our business need states that the information it contains must be isolated from other database transactions until the user logs out. This information should be displayed in part on different Web pages. This calls for creating a clone. One thing to pay attention to while cloning is that any operation performed on the copied data will also occur on the original data because references to data objects are copied, not the objects themselves. In some cases, this might be unacceptable. In this case, our class would also implement a Serializable interface.
Now we would just write our object out to a stream and reread it, making the two objects completely independent of each other. This again assumes that all the objects contained in this class are themselves serializable. Listing 3 provides the deepClone() method.
I've discussed five creation patterns here. If you are interested in learning more about patterns, I would recommend reading one of the many books available about design patterns.
|Neil Hornbeck 09/09/04 07:47:15 AM EDT|
The source listing is for a Java card applet, which doesn't seem correct for this article.
As more and more data is generated from a variety of connected devices, the need to get insights from this data and predict future behavior and trends is increasingly essential for businesses. Real-time stream processing is needed in a variety of different industries such as Manufacturing, Oil and Gas, Automobile, Finance, Online Retail, Smart Grids, and Healthcare. Azure Stream Analytics is a fully managed distributed stream computation service that provides low latency, scalable processing of streaming data in the cloud with an enterprise grade SLA. It features built-in integration with Azur...
Aug. 27, 2015 03:45 PM EDT
WebRTC has had a real tough three or four years, and so have those working with it. Only a few short years ago, the development world were excited about WebRTC and proclaiming how awesome it was. You might have played with the technology a couple of years ago, only to find the extra infrastructure requirements were painful to implement and poorly documented. This probably left a bitter taste in your mouth, especially when things went wrong.
Aug. 27, 2015 02:45 PM EDT Reads: 374
As more intelligent IoT applications shift into gear, they’re merging into the ever-increasing traffic flow of the Internet. It won’t be long before we experience bottlenecks, as IoT traffic peaks during rush hours. Organizations that are unprepared will find themselves by the side of the road unable to cross back into the fast lane. As billions of new devices begin to communicate and exchange data – will your infrastructure be scalable enough to handle this new interconnected world?
Aug. 27, 2015 02:15 PM EDT
SYS-CON Events announced today that IceWarp will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. IceWarp, the leader of cloud and on-premise messaging, delivers secured email, chat, documents, conferencing and collaboration to today's mobile workforce, all in one unified interface
Aug. 27, 2015 02:00 PM EDT Reads: 319
Too often with compelling new technologies market participants become overly enamored with that attractiveness of the technology and neglect underlying business drivers. This tendency, what some call the “newest shiny object syndrome,” is understandable given that virtually all of us are heavily engaged in technology. But it is also mistaken. Without concrete business cases driving its deployment, IoT, like many other technologies before it, will fade into obscurity.
Aug. 27, 2015 01:00 PM EDT Reads: 280
Consumer IoT applications provide data about the user that just doesn’t exist in traditional PC or mobile web applications. This rich data, or “context,” enables the highly personalized consumer experiences that characterize many consumer IoT apps. This same data is also providing brands with unprecedented insight into how their connected products are being used, while, at the same time, powering highly targeted engagement and marketing opportunities. In his session at @ThingsExpo, Nathan Treloar, President and COO of Bebaio, will explore examples of brands transforming their businesses by t...
Aug. 27, 2015 11:30 AM EDT
The Internet of Things (IoT) is about the digitization of physical assets including sensors, devices, machines, gateways, and the network. It creates possibilities for significant value creation and new revenue generating business models via data democratization and ubiquitous analytics across IoT networks. The explosion of data in all forms in IoT requires a more robust and broader lens in order to enable smarter timely actions and better outcomes. Business operations become the key driver of IoT applications and projects. Business operations, IT, and data scientists need advanced analytics t...
Aug. 27, 2015 10:45 AM EDT Reads: 306
SYS-CON Events announced today that Micron Technology, Inc., a global leader in advanced semiconductor systems, will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Micron’s broad portfolio of high-performance memory technologies – including DRAM, NAND and NOR Flash – is the basis for solid state drives, modules, multichip packages and other system solutions. Backed by more than 35 years of technology leadership, Micron's memory solutions enable the world's most innovative computing, consumer,...
Aug. 27, 2015 10:00 AM EDT Reads: 117
Through WebRTC, audio and video communications are being embedded more easily than ever into applications, helping carriers, enterprises and independent software vendors deliver greater functionality to their end users. With today’s business world increasingly focused on outcomes, users’ growing calls for ease of use, and businesses craving smarter, tighter integration, what’s the next step in delivering a richer, more immersive experience? That richer, more fully integrated experience comes about through a Communications Platform as a Service which allows for messaging, screen sharing, video...
Aug. 27, 2015 06:15 AM EDT Reads: 497
With the proliferation of connected devices underpinning new Internet of Things systems, Brandon Schulz, Director of Luxoft IoT – Retail, will be looking at the transformation of the retail customer experience in brick and mortar stores in his session at @ThingsExpo. Questions he will address include: Will beacons drop to the wayside like QR codes, or be a proximity-based profit driver? How will the customer experience change in stores of all types when everything can be instrumented and analyzed? As an area of investment, how might a retail company move towards an innovation methodolo...
Aug. 26, 2015 10:00 AM EDT Reads: 365
SYS-CON Events announced today that Pythian, a global IT services company specializing in helping companies leverage disruptive technologies to optimize revenue-generating systems, has been named “Bronze Sponsor” of SYS-CON's 17th Cloud Expo, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Founded in 1997, Pythian is a global IT services company that helps companies compete by adopting disruptive technologies such as cloud, Big Data, advanced analytics, and DevOps to advance innovation and increase agility. Specializing in designing, imple...
Aug. 26, 2015 08:00 AM EDT Reads: 149
Akana has announced the availability of the new Akana Healthcare Solution. The API-driven solution helps healthcare organizations accelerate their transition to being secure, digitally interoperable businesses. It leverages the Health Level Seven International Fast Healthcare Interoperability Resources (HL7 FHIR) standard to enable broader business use of medical data. Akana developed the Healthcare Solution in response to healthcare businesses that want to increase electronic, multi-device access to health records while reducing operating costs and complying with government regulations.
Aug. 26, 2015 07:00 AM EDT
SYS-CON Events announced today that HPM Networks will exhibit at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. For 20 years, HPM Networks has been integrating technology solutions that solve complex business challenges. HPM Networks has designed solutions for both SMB and enterprise customers throughout the San Francisco Bay Area.
Aug. 3, 2015 06:45 PM EDT Reads: 772
For IoT to grow as quickly as analyst firms’ project, a lot is going to fall on developers to quickly bring applications to market. But the lack of a standard development platform threatens to slow growth and make application development more time consuming and costly, much like we’ve seen in the mobile space. In his session at @ThingsExpo, Mike Weiner, Product Manager of the Omega DevCloud with KORE Telematics Inc., discussed the evolving requirements for developers as IoT matures and conducted a live demonstration of how quickly application development can happen when the need to comply wit...
Aug. 2, 2015 11:15 AM EDT Reads: 537
The Internet of Everything (IoE) brings together people, process, data and things to make networked connections more relevant and valuable than ever before – transforming information into knowledge and knowledge into wisdom. IoE creates new capabilities, richer experiences, and unprecedented opportunities to improve business and government operations, decision making and mission support capabilities.
Aug. 1, 2015 10:00 AM EDT Reads: 467
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at @ThingsExpo, James Kirkland, Red Hat's Chief Architect for the Internet of Things and Intelligent Systems, described how to revolutionize your archit...
Jul. 30, 2015 07:30 PM EDT Reads: 1,554
MuleSoft has announced the findings of its 2015 Connectivity Benchmark Report on the adoption and business impact of APIs. The findings suggest traditional businesses are quickly evolving into "composable enterprises" built out of hundreds of connected software services, applications and devices. Most are embracing the Internet of Things (IoT) and microservices technologies like Docker. A majority are integrating wearables, like smart watches, and more than half plan to generate revenue with APIs within the next year.
Jul. 30, 2015 02:30 PM EDT Reads: 267
Growth hacking is common for startups to make unheard-of progress in building their business. Career Hacks can help Geek Girls and those who support them (yes, that's you too, Dad!) to excel in this typically male-dominated world. Get ready to learn the facts: Is there a bias against women in the tech / developer communities? Why are women 50% of the workforce, but hold only 24% of the STEM or IT positions? Some beginnings of what to do about it! In her Opening Keynote at 16th Cloud Expo, Sandy Carter, IBM General Manager Cloud Ecosystem and Developers, and a Social Business Evangelist, d...
Jul. 30, 2015 12:00 PM EDT Reads: 2,213
In his keynote at 16th Cloud Expo, Rodney Rogers, CEO of Virtustream, discussed the evolution of the company from inception to its recent acquisition by EMC – including personal insights, lessons learned (and some WTF moments) along the way. Learn how Virtustream’s unique approach of combining the economics and elasticity of the consumer cloud model with proper performance, application automation and security into a platform became a breakout success with enterprise customers and a natural fit for the EMC Federation.
Jul. 30, 2015 09:00 AM EDT Reads: 2,305
The Internet of Things is not only adding billions of sensors and billions of terabytes to the Internet. It is also forcing a fundamental change in the way we envision Information Technology. For the first time, more data is being created by devices at the edge of the Internet rather than from centralized systems. What does this mean for today's IT professional? In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists addressed this very serious issue of profound change in the industry.
Jul. 29, 2015 03:00 PM EDT Reads: 1,436