Skip to main content

Singleton Pattern

Lazy Initialization:-The instantiation of an object can be delayed until it is actually needed.

Usage: This especially beneficial when the constructor is doing a costly job like, accessing a remote database.

Example:

This code demonstrates how the Singleton pattern can be used to create a counter to provide unique sequential numbers, such as might be required for use as primary keys in a

Database:


 

Sequence.java


 

public class Sequence {

private static Sequence instance;

private static int counter;

private Sequence()

{

counter = 0; // May be necessary to obtain

// starting value elsewhere...

}

public static synchronized Sequence getInstance()

{

if(instance==null) // Lazy instantiation

{

instance = new Sequence();

}

return instance;

}

public static synchronized int getNext()

{

return ++counter;

}

}


 

Some things to note about this implementation:

  • Synchronized methods are used to ensure that the class is thread-safe.
  • This class cannot be subclassed because the constructor is private. This may or may not be a good thing depending on the resource being protected. To allow subclassing, the visibility of the constructor should be changed to protected.
  • Object serialization can cause problems; if a Singleton is serialized and then deserialized more than once, there will be multiple objects and not a singleton
Labels:

Popular posts from this blog

Design Patterns (TID)

The pattern is an organised way of solving some specific class of problems. These patterns come in to the picture at analysis and high-level-design phase. The first step of applying one pattern to the code base is first to understand the find the vector of change in the code base. Next step is to isolate the things that are subject to change form the things that are not. That is adding a layer of abstraction to the code. The goal of design patterns is isolating the changes in your code. Understand Inheritance and Composition as a solution to a specific class of problems. Inheritance : - It allows you to express differences in behavior (that's the thing that changes) in objects that all have the same interface (that's what stays the same). Composition : - Composition can also be considered a pattern, since it allows you to change—dynamically or statically—the objects that implement your class, and thus the way that class works. Some principles of designing the c...
Read more

Adobe Firefly

Adobe Firefly is designed to help developers create custom applications more quickly and easily. The platform is built on top of Adobe's existing Experience Cloud, which provides a range of tools for managing customer data and creating personalized experiences. One of the key features of Adobe Firefly is its ability to integrate with a wide range of other technologies and services. This means that developers can use the platform to build applications that connect with everything from social media platforms to IoT devices. Another important aspect of Adobe Firefly is its focus on speed and efficiency. The platform includes a range of pre-built components and templates that developers can use to quickly create new applications. It also includes a range of tools for testing and debugging applications, which can help to speed up the development process. Overall, Adobe Firefly looks like an exciting new platform for developers who are looking to create custom applications quickly and ef...
Read more

Primitive Obsession with Example

Primitive Obsession is the name of a code smell that occurs when we use primitive data types to represent domain ideas. For example, we use a string to represent a message or an integer to represent an amount of money. For Example: Code with Primitive Obsession // primitiveObsession.java public class primitiveObsession { public static void main ( String args []) { Integer [] cityPopulations = { 13000000 , // London 21903623 , // New York 12570000 , // Tokyo 1932763 , // Stockholm 1605602 , // Barcelona 4119190 // Sydney }; for ( Integer cityPopulation : cityPopulations ) { System . out . println ( cityPopulation ); } } } public class City { private final String name ; private final int population ; private final Continent continent ; public String getName () { return name ; } public int getPopulation () { return population ; } public Continent ge...
Read more