|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.
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management...
Feb. 7, 2016 03:30 PM EST Reads: 370
The cloud promises new levels of agility and cost-savings for Big Data, data warehousing and analytics. But it’s challenging to understand all the options – from IaaS and PaaS to newer services like HaaS (Hadoop as a Service) and BDaaS (Big Data as a Service). In her session at @BigDataExpo at @ThingsExpo, Hannah Smalltree, a director at Cazena, will provide an educational overview of emerging “as-a-service” options for Big Data in the cloud. This is critical background for IT and data profes...
Feb. 7, 2016 02:45 PM EST Reads: 138
SYS-CON Events announced today that VAI, a leading ERP software provider, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. VAI (Vormittag Associates, Inc.) is a leading independent mid-market ERP software developer renowned for its flexible solutions and ability to automate critical business functions for the distribution, manufacturing, specialty retail and service sectors. An IBM Premier Business Part...
Feb. 7, 2016 02:00 PM EST Reads: 555
SYS-CON Events announced today that Alert Logic, Inc., the leading provider of Security-as-a-Service solutions for the cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Alert Logic, Inc., provides Security-as-a-Service for on-premises, cloud, and hybrid infrastructures, delivering deep security insight and continuous protection for customers at a lower cost than traditional security solutions. Ful...
Feb. 7, 2016 01:45 PM EST Reads: 360
Fortunately, meaningful and tangible business cases for IoT are plentiful in a broad array of industries and vertical markets. These range from simple warranty cost reduction for capital intensive assets, to minimizing downtime for vital business tools, to creating feedback loops improving product design, to improving and enhancing enterprise customer experiences. All of these business cases, which will be briefly explored in this session, hinge on cost effectively extracting relevant data from ...
Feb. 7, 2016 01:30 PM EST
With the Apple Watch making its way onto wrists all over the world, it’s only a matter of time before it becomes a staple in the workplace. In fact, Forrester reported that 68 percent of technology and business decision-makers characterize wearables as a top priority for 2015. Recognizing their business value early on, FinancialForce.com was the first to bring ERP to wearables, helping streamline communication across front and back office functions. In his session at @ThingsExpo, Kevin Roberts...
Feb. 7, 2016 12:00 PM EST Reads: 342
SYS-CON Events announced today that Interoute, owner-operator of one of Europe's largest networks and a global cloud services platform, has been named “Bronze Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2015 at the Javits Center in New York, New York. Interoute is the owner-operator of one of Europe's largest networks and a global cloud services platform which encompasses 12 data centers, 14 virtual data centers and 31 colocation centers, with connections to 195 ad...
Feb. 7, 2016 11:30 AM EST Reads: 344
With an estimated 50 billion devices connected to the Internet by 2020, several industries will begin to expand their capabilities for retaining end point data at the edge to better utilize the range of data types and sheer volume of M2M data generated by the Internet of Things. In his session at @ThingsExpo, Don DeLoach, CEO and President of Infobright, will discuss the infrastructures businesses will need to implement to handle this explosion of data by providing specific use cases for filte...
Feb. 7, 2016 10:15 AM EST Reads: 106
As enterprises work to take advantage of Big Data technologies, they frequently become distracted by product-level decisions. In most new Big Data builds this approach is completely counter-productive: it presupposes tools that may not be a fit for development teams, forces IT to take on the burden of evaluating and maintaining unfamiliar technology, and represents a major up-front expense. In his session at @BigDataExpo at @ThingsExpo, Andrew Warfield, CTO and Co-Founder of Coho Data, will dis...
Feb. 7, 2016 07:00 AM EST Reads: 119
SYS-CON Events announced today that Fusion, a leading provider of cloud services, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Fusion, a leading provider of integrated cloud solutions to small, medium and large businesses, is the industry's single source for the cloud. Fusion's advanced, proprietary cloud service platform enables the integration of leading edge solutions in the cloud, including clou...
Feb. 6, 2016 03:30 PM EST Reads: 718
Most people haven’t heard the word, “gamification,” even though they probably, and perhaps unwittingly, participate in it every day. Gamification is “the process of adding games or game-like elements to something (as a task) so as to encourage participation.” Further, gamification is about bringing game mechanics – rules, constructs, processes, and methods – into the real world in an effort to engage people. In his session at @ThingsExpo, Robert Endo, owner and engagement manager of Intrepid D...
Feb. 5, 2016 09:00 PM EST Reads: 785
Eighty percent of a data scientist’s time is spent gathering and cleaning up data, and 80% of all data is unstructured and almost never analyzed. Cognitive computing, in combination with Big Data, is changing the equation by creating data reservoirs and using natural language processing to enable analysis of unstructured data sources. This is impacting every aspect of the analytics profession from how data is mined (and by whom) to how it is delivered. This is not some futuristic vision: it's ha...
Feb. 2, 2016 02:00 PM EST Reads: 409
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.
Feb. 2, 2016 04:30 AM EST Reads: 851
Learn how IoT, cloud, social networks and last but not least, humans, can be integrated into a seamless integration of cooperative organisms both cybernetic and biological. This has been enabled by recent advances in IoT device capabilities, messaging frameworks, presence and collaboration services, where devices can share information and make independent and human assisted decisions based upon social status from other entities. In his session at @ThingsExpo, Michael Heydt, founder of Seamless...
Feb. 1, 2016 05:00 AM EST Reads: 940
The IoT's basic concept of collecting data from as many sources possible to drive better decision making, create process innovation and realize additional revenue has been in use at large enterprises with deep pockets for decades. So what has changed? In his session at @ThingsExpo, Prasanna Sivaramakrishnan, Solutions Architect at Red Hat, discussed the impact commodity hardware, ubiquitous connectivity, and innovations in open source software are having on the connected universe of people, thi...
Jan. 31, 2016 09:00 PM EST Reads: 726
WebRTC: together these advances have created a perfect storm of technologies that are disrupting and transforming classic communications models and ecosystems. In his session at WebRTC Summit, Cary Bran, VP of Innovation and New Ventures at Plantronics and PLT Labs, provided an overview of this technological shift, including associated business and consumer communications impacts, and opportunities it may enable, complement or entirely transform.
Jan. 31, 2016 07:15 PM EST Reads: 1,146
There are so many tools and techniques for data analytics that even for a data scientist the choices, possible systems, and even the types of data can be daunting. In his session at @ThingsExpo, Chris Harrold, Global CTO for Big Data Solutions for EMC Corporation, showed how to perform a simple, but meaningful analysis of social sentiment data using freely available tools that take only minutes to download and install. Participants received the download information, scripts, and complete end-t...
Jan. 31, 2016 10:00 AM EST Reads: 1,216
For manufacturers, the Internet of Things (IoT) represents a jumping-off point for innovation, jobs, and revenue creation. But to adequately seize the opportunity, manufacturers must design devices that are interconnected, can continually sense their environment and process huge amounts of data. As a first step, manufacturers must embrace a new product development ecosystem in order to support these products.
Jan. 31, 2016 10:00 AM EST Reads: 812
Manufacturing connected IoT versions of traditional products requires more than multiple deep technology skills. It also requires a shift in mindset, to realize that connected, sensor-enabled “things” act more like services than what we usually think of as products. In his session at @ThingsExpo, David Friedman, CEO and co-founder of Ayla Networks, discussed how when sensors start generating detailed real-world data about products and how they’re being used, smart manufacturers can use the dat...
Jan. 30, 2016 07:45 PM EST Reads: 790
When it comes to IoT in the enterprise, namely the commercial building and hospitality markets, a benefit not getting the attention it deserves is energy efficiency, and IoT’s direct impact on a cleaner, greener environment when installed in smart buildings. Until now clean technology was offered piecemeal and led with point solutions that require significant systems integration to orchestrate and deploy. There didn't exist a 'top down' approach that can manage and monitor the way a Smart Buildi...
Jan. 30, 2016 03:45 PM EST Reads: 1,268