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A factory method design pattern in Java lets you create objects without revealing their concrete classes, which makes it possible to change the class of the object that gets created at run time and to extend the functionality of an existing class by substituting subclasses at run time. If you haven’t used it before, the Factory Method Design Pattern in Java may seem like just another one of those solutions that are hard to understand and will never be useful to you, but you couldn’t be more wrong. In fact, this design pattern has many uses that will help you save time and effort throughout your programming career, as well as make your code more readable and maintainable in the long term. Here are some examples of how to use it, along with additional information about its purpose and application. The factory method design pattern allows us to create objects without specifying the exact class of the object that will be created. It enables us to write and test small pieces of code without having to create an instance of the object we are actually interested in at that time, which can lead to improved reusability and testability. We just need to focus on what the object will do, not how it will do it – all the latter is hidden behind an interface that we define when we implement the factory method pattern.
Why do we need a Factory Method Design Pattern?
We all know that there are different kinds of design patterns available to use and one of those patterns is the factory method. Why do we need a factory method design pattern? What is its usage? In order to answer these questions, let us get a brief introduction to what is factory method. Basically, when we look at real-world scenarios, it becomes clear that most of the time an instance can be created either by using a new operator or by calling some specific functions. Let us take an example as a car manufacturer where car manufacturer has made various types of cars with different features, colors, etc. Now if we want to buy a car from them then we have two options: 1) Buy directly from them or 2) Buy from their authorized dealer. Now both ways have their own advantages and disadvantages but here I am talking about the first option only because if you buy directly from them then you will get a great discount on your car whereas if you buy through their authorized dealer then you will have to pay full price for your car but still it will save your lots of money as compared to buying directly from them because no matter how many times you ask for the discount they won’t give you any discount.
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So basically there are two ways for creating instances i.e. by using a new operator or by calling some specific function. Now, why do we need a factory method design pattern? The factory method allows us to create instances without specifying the exact class names so it gives flexibility to client code. As mentioned above that there are two ways for creating instances i.e. by using a new operator or by calling some specific function so when client code asks for object creation then factory method implementation decides which way should be used for creating an object based on input parameter(s). If input parameter(s) match with the argument(s) passed while instantiating class then objects will be created via constructor otherwise objects will be created via a static function call.
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How to Implement Factory Method Design Pattern in Java?
We will start by taking a look at an example, then explore some of its benefits and use cases. Finally, we’ll look at some other ways to solve factory method problems in java. This way, you’ll know when you should use it, and what are other possible solutions. So if you want to learn how to implement factory method design patterns in java, let’s get started! What is the factory method design pattern?: The main idea behind factory methods is that instead of creating new objects directly, we ask an object for another object (usually of a different type). The factory does all the work for us: finding or creating and initializing objects as needed. It can also return any type depending on input parameters, allowing us to create a single interface for all different types of objects that need to be created. In short, it allows for code reuse through polymorphism.
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Benefits of using factory method design pattern in java: One of its biggest advantages is that it reduces complexity and makes your code more readable. Instead of having multiple constructors with tons of arguments, you have a single constructor with one argument which returns an object from a predefined set (the factory). Another benefit is that it reduces duplication. Instead of duplicating complex logic across multiple constructors, we encapsulate everything into one place—the factory method. Use cases for factory method design pattern in java: Let’s take a look at some common examples where you might want to use factory methods. 1) Creating database connections: If you have a connection pool in your application, there’s no reason why each class shouldn’t simply request connections from it rather than make their own connections. 2) Creating loggers/output streams/file handlers/etc.: A similar case to our first example; classes don’t need to make their own loggers, they just request them from somewhere else. 3) Parsing XML/JSON data: If we need classes that parse data returned by HTTP requests or databases, why not put them together?
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Example of Factory Method Design Pattern
A factory method is a special class used to create objects. It looks like a static method and is called a regular instance method, but it creates and returns an instance of some other class. The factory creates an object that can be used by clients without having to know what type of object it actually is (encapsulation). A factory might also have more than one way to create an object. If you don’t care about client code calling your methods, use an abstract factory java instead. Most of these patterns require multiple inheritances and/or runtime polymorphism because they need to be able to create several different types of objects depending on input or on configuration data at runtime. This pattern was invented by Gamma et al. in 1995, though there are many older examples of similar techniques. In their book Design Patterns, Gamma et al. call it the factory method.
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Martin Fowler calls it abstract factory java and Kent Beck calls it Factory Method. Eric Evans calls it factory interface in Domain-Driven Design. Other languages may have different names for it; however, they all refer to essentially the same concept. There are two main advantages to using a factory: Encapsulation: Clients only interact with simple classes with well-defined interfaces. They do not depend on how those classes are implemented or even if they will continue to exist in future versions of our software. Instead, clients simply request instances from factories and let them worry about creating new instances. Reusability: Factories allow us to easily reuse functionality as we see fit by creating new implementations of production classes.
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To create Instances with a Variable Set of Attributes
Sometimes, you need to create an object with certain attributes—such as font size or color. Rather than hard-coding these values into your code, use factory methods to do it for you. That way, if you ever need to change a value, all you have to do is change one line of code (the method call) instead of multiple lines throughout your app. The following example illustrates how that might work: public class Product { private String name; private double price; public Product(String name, double price) {…} public static final int LARGE = 0; public static final int MEDIUM = 1; … } Now, regardless of whether a customer buys a large or medium product at our hypothetical store, we’ll know what size it is. We can add even more details by using nested classes: public class Product { private String name; private double price; public Product(String name, double price) {…} public static final int LARGE = 0; public static final int MEDIUM = 1; protected static enum Size{LARGE, MEDIUM}; … } Now we can also determine if a given product is available in different sizes. To make sure only valid products are sold at our store, we can validate any objects passed to us from customers against our definition of what constitutes a valid product. To create instances with variable behavior: In addition to creating objects with specific attributes, factories allow us to control how those objects behave after they’re created.
When you have Different Types of Objects Implementing the Same Interface
You can’t instantiate objects of that interface, since they don’t have any concrete class to get their parameters from. You can simply implement a static method on each concrete implementation of your interface. This method will be responsible for returning an instance of a class implementing a said interface, depending on its name parameter. When you want to provide alternative implementations of an algorithm or type mapping, at runtime: This is a pretty standard use case for pattern matching (and probably also its most common). For example, if we have 2 classes for binary trees with identical constructors and members but different leaf types. We could write a factory method that would accept a leaf type as input and return either one of those two classes based on that parameter. If you need to create objects dynamically based on some logic: In general, it’s not advised to do so unless there are no other options. But sometimes, when we need these dynamic instances only temporarily during execution time, having them created by factory methods makes sense. One such example would be creating separate threads based on some condition – like only runnable threads should remain running. In these cases, we’d create Thread instances by calling factory methods which check whether our conditions are met before actually creating new threads.
To create a new kind of Object Without Modifying the Class that creates it
This is perhaps one of the factory pattern’s most common uses. Let’s take a look at a real-world example: suppose you have an application for sending and receiving text messages. You might use two separate classes for your SendSMS class and ReceiveSMS class, where ReceiveSMS is a subclass of SendSMS. The problem with doing things that way—aside from creating duplicated code—is that if you want to add another kind of SMS, such as an e-mail, voice mail, or fax message, you will have to modify your SendSMS class and all its subclasses to accommodate it. That’s where factories come into play. Instead of having many different types of senders, you can create a SenderFactory, which makes new instances of Sender objects depending on what type of message they send. For example, if you wanted to add support for email messages, then your SenderFactory would create EmailSender objects instead of SendSMS objects.
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This allows you to keep your existing classes unchanged while adding new functionality without modifying them at all! To make sure we get our hands on only those factories we need (and not every single factory registered), we can use dependency injection frameworks like Guice or Spring AOP framework. In addition, factories are useful when we don’t know beforehand how many different kinds of objects we may need. In some cases, there could be dozens or even hundreds of potential objects, so using factory methods saves us from writing duplicate code and helps prevent bugs caused by typos. To change an object’s behavior during runtime: Another typical use case for factories is to change how certain classes behave during runtime. This is useful when we want to substitute one implementation with another based on certain conditions being met—for example, changing how a class behaves based on whether it has been instantiated yet or not.
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To use Subclasses as Factories for their Superclass
One of the simplest ways to use a factory method is to make subclasses act as factories for their superclass. The Visitor pattern and Strategy pattern are two well-known examples of frameworks where subclass-as-factory is used. To facilitate more than one kind of object in a collection: A factory method can be used when there’s more than one type of object that should be allowed into a collection, but you don’t want them to interact with each other; sometimes you don’t even know what types are allowed beforehand. This is similar to polymorphism, but you are ensuring that all objects coming from that factory share a common interface, or inherit from some common parent class. For example, let’s say you have an ArrayList of Employee objects. Some employees are managers, while others aren’t; your manager Employees will need access to certain protected methods that non-managers won’t (e.g., fire employee()). If you didn’t use a factory method here, then every Employee would need access to these protected methods—which is bad design because it violates encapsulation and information hiding principles.
With a simple factory method though, only managers will have access to these protected methods without changing any code! To create several instances of a singleton class: When you want just one instance of a class, and no more, then using a singleton is often overkill. In such cases, it’s better to just create an instance via static factory method rather than defining getInstance() methods on every singleton class. To create classes whose instances are singletons by default: You can also define static factory methods on interfaces or abstract classes which return concrete implementations instead of singletons. Doing so makes those classes’ instances singletons by default, which may not always be desirable. To simplify instantiation logic for complex classes: Sometimes we end up creating really complex constructors with lots of arguments that simply become hard to read at times.
To Generate Derived Classes at Runtime Based on Run-time Information
Use class factories to create classes from a base class and one or more run-time values. A factory object is responsible for creating derived classes at runtime. This design pattern allows derived classes to be created without code being duplicated across classes that perform similar tasks but require different types of data as parameters. It does so by providing an interface that allows subclasses to specify which type of data will be passed as a parameter when they are constructed. This design pattern is called Factory Method. The UML diagram below shows how class factories can be used:
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This design pattern has been implemented in many programming languages including C++, Python, Ruby, and Java. In C++ it is known as the Template method; in Python, it is known as Abstract Factory; in Ruby, it is known as Module; while in Java it is known as abstract factory java method (AFM). The following sections provide examples of how to implement AFM using various programming languages. A factory class that can be used to create several related objects is called a class factory. The example below shows a base class Shape with derived classes Rectangle and Circle: public abstract class Shape {
For Building a Hierarchy of Classes Without Using Multiple Inheritances
The use of factory methods is a way to avoid multiple inheritances while gaining almost all of its benefits. Consider a class that is abstract, which cannot be instantiated, but has subclasses that can be instantiated. Here’s how it works: one subclass contains an abstract method called makeInstance(), which takes no arguments and returns an instance of itself. The other subclass contains a concrete implementation of makeInstance() (one with all non-abstract methods implemented), with no name—that means it doesn’t really return anything meaningful from make-instance(). Instead, when you ask for an instance using make-instance(), it simply creates one of itself. This is a perfect example of what we call factory methods.
You are requesting an object, but not specifying what kind of object; instead, you are asking for whatever type of object should happen to be returned by some other code. In our case, that code is contained within our second subclass. We’ll see below how useful it is to have a single point of control over creating objects, even if those objects will eventually go on to contain lots of states or behavior. It would be awkward at best if different parts of your application were creating instances of different classes. For example, consider an application where you need to use several specialized types of database connection pools. In such a situation, if each part created its own pool, there would likely be subtle differences between them that could cause bugs later on down the road. To avoid these problems, we often choose to create shared pools at startup time and pass around references to them as needed throughout our application.
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For Code Reuse When You Cannot Modify The Code From Which Instances Are Made
Code reuse is a primary benefit of using object-oriented programming, but sometimes you don’t have control over a class that you want to use as an instance. Or it may not be practical to modify its code because of backward compatibility issues or other concerns. In such cases, a factory method allows you to create instances without modifying existing classes. You can even implement a factory method from scratch when you need code reuse that’s so specific it makes sense only for your own application and source code. Here are some examples of those situation #1: If a particular class must exist before you can instantiate it: A classic example of needing a factory method occurs with database connections. Many applications require access to a database at runtime, but creating database connections requires setting up connection strings and credentials—which means creating them ahead of time.
The best way to solve this problem is by implementing a static factory method that creates new connections based on information passed into it (for example, username/password pairs). Once created, they’re ready for use whenever needed. #2: To make objects easier to manage and more flexible: Another common reason for using a factory method is when you want to allow users of your code to specify which type of object they want. For example, suppose you have an Employee class whose constructor accepts both first name and last name parameters; however, some employees do not have last names. Instead of forcing every user of your Employee class to supply both first name and last name every time they create an employee, let them pass just their first name (and let your factory method deal with whether or not there’s also the last name). This approach also makes it easy for users to change their minds later about what kind of employee they really need; all they have to do is change one line in their program.
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Conclusion
In my experience, I’ve found that designing a program using Factory methods is often much easier than creating a program where classes all have to be subclasses of each other. The ability to separate how a class is created from what it does allows for an easy form of code re-use without much more work on your part. In addition, because you can now create multiple factory classes with different behaviors, you can quickly and easily swap out parts of your program to try new features and ideas without actually changing any core logic. When working with objects in Java, it’s important to remember that when you extend a class, you are not just inheriting its behavior, but taking on its responsibilities as well. If you are interested to learn new coding skills, the Entri app will help you to acquire them very easily. Entri app is following a structural study plan so that the students can learn very easily. If you don’t have a coding background, it won’t be any problem. You can download the Entri app from the google play store and enroll in your favorite course.
