Design Patterns: Singleton in Java

Design Patterns are beneficial for programmers when they need to utilize the best available practices in object-oriented software development. Design Patterns can be understood as well-proved and tried and tested solutions for solving the design problem at hand. Design Systems describes the problem, the solution, when to apply the solution, and its consequences. In a way, Design Patterns can be thought of as different templates that software developers can implement when they are solving specific object-oriented design problems. 

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Some of the features of using Design patterns in Java as compared to coding from scratch include: 

• Design Patterns are already defined and implemented. As a result, they provide a standard approach to solve repetitive problems. In that sense, it helps programmers save a lot of time and effort. 
• Using Design Patterns ensures the reusability of your piece of code, which leads to high maintainability and robustness of your Java code. All of this then reduces the total cost of ownership (TCO) of the software at hand. 
• Design Patterns make the code easy to read and understand, which leads to faster communication and seamless software development. 

Java programming language offers various Design Patterns for programmers and developers, which can broadly be broken down into three categories: 

• Creational Design Patterns
• Structural Design Patterns
• Behavioural Design Patterns

All of these patterns are used for different use cases and purposes. Through this article, let’s talk about one kind of Design Pattern in Java – Singleton Design Pattern, which falls under the Creational Design Patterns category. 

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Singleton Design Pattern in Java

Singleton Design Pattern belongs to the Creational Design Pattern category. It ensures that a class only has one instance, providing this instance with a global access point. In doing so, the Singleton Design Pattern solves two problems at once – these include: 

1. It ensures that a given class has only one instance. 

This is important to consider, especially when working on shared resources, like a database or a file. Imagine that you created an object, but after a while, decided to create a new one. In the Singleton Design Pattern, instead of receiving a new object, you’ll get the one you already made. That way, this Design Pattern ensures no redundancy of objects and that a class has only one instance. This behaviour is impossible to replicate with constructors because constructor calls must always return a new object. 

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2. Provides a global access point to the particular instance.

The global variables that you use to store essential objects are pretty handy. They are also equally unsafe since any piece of code has the power to overwrite the contents of your global variables, leading to an erroneous piece of code for you. Just like global variables, Singleton Patterns allows you to access different objects from anywhere in the program. However, unlike global variables, Singleton Patterns secures that instance from being overwritten by another program.

Nowadays, the Singleton Design Pattern is so widely used and prevalent that programmers may call something Singleton even if it solves just one of the above-listed problems. All the implementations of Singleton Design Patterns have the following two steps in common: 

• Making the default constructor private to prevent other classes and objects from using new operators with Singleton classes. 
• Building a static creation method to function as a constructor. This method, then, calls the private constructor to create an object and saves it in a static field. All the upcoming calls to this particular method now return the cached object. 

The government’s functioning is an excellent real-life example to understand how Singleton Design Patterns work. Regardless of the personal identities of the individuals who constitute the governments, the title, “The Government of X”, is the global point of access that identifies the group of people being talked about.

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Implementing Singleton Design Pattern in Java

Please go through the following list of steps to implement your own Singleton Design Pattern in Java: 

• Add a private static field to the class where you wish to store the singleton instance. 
• To get the appropriate singleton instance, you must declare a public static method. 
• Now, you need to execute “lazy initialization” inside the static method. This should essentially develop a new object on its first call and place that into the static field. The static method must always return that particular instance on all subsequent calls.

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• Make the constructor private. The class’s static method will still be able to call the constructor, but not the other objects.
• Please go over the client code and replace all direct calls to Singleton’s constructor with calls to its static creation method.

In Conclusion

Java is a highly diverse and influential programming language, and it has emerged as a foundation for most of the web and desktop applications in use today. It provides several features and strategies that programmers can use to develop better-performing software in an optimized fashion. Design Patterns are one such strategy adopted by Java programmers to make their codes readable, reusable, and understandable. 

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