Singleton Class in Kotlin - Software Development PDF Download

Singleton Class in Kotlin

Singleton Class in Kotlin, also known as the Singleton Object, ensures that only one instance of the class can be created and utilized universally. Repeatedly creating multiple objects of the same class results in the allocation of separate memory spaces for each object. Hence, it is more efficient to instantiate a single object and reuse it.

Kotlin

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In the above example, both objects have distinct addresses, resulting in memory wastage. In the subsequent program, we employ a singleton class to address this issue.

By utilizing an object instead of a class, Kotlin automatically applies the Singleton pattern, efficiently allocating a single memory space. In Java, a singleton class is created by defining a class named Singleton, whereas in Kotlin, the 'object' keyword is used. The 'object' class can comprise functions, properties, and the 'init' method, but it does not allow a constructor. If initialization is required, the 'init' method can be utilized, and the 'object' can be nested inside a class. Methods and member variables within the singleton class are accessed using the class name, akin to companion objects.

Singleton Object and Companion Objects

• A singleton object in Kotlin is an object that is declared using the "object" keyword and can have properties and methods.
• Companion objects are similar to static methods in Java and are declared using the "companion object" keyword.

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Properties of Singleton Class

• Only one instance: The singleton class has only one instance, ensuring there is a unique object of that class.
• Globally accessible: The instance of the singleton class is accessible globally, allowing all classes to use it as needed.
• Constructor not allowed: Instead of a constructor, the init method is used to initialize member variables of the singleton class.

• Singleton Class Characteristics:
  • The singleton class is designed to have only one instance, achieved by embedding an instance of the class within the class itself.
  • The instance of the singleton class must be globally accessible, allowing all classes to utilize it.
  • Unlike regular classes, a constructor is not permitted in a singleton class. Initialization of member variables is usually done through an init method.
• Importance of Singleton Objects In Android:
  • Singleton objects play a crucial role in Android development by ensuring that only one instance of a particular object exists throughout the entire application.
  • Examples of the significance of singleton objects in Android include:
  • Use Case 1 - Retrofit in Network Requests:
    • When utilizing Retrofit for network requests in an app, it is essential to have a single instance of Retrofit. This single instance contains properties like Gson Converter and Moshy Converter, which should be reused to prevent unnecessary resource consumption and time delays.
  • Use Case 2 - Repository in MVVM Architecture:
    • In the MVVM architecture, repositories remain constant. Therefore, creating only one instance of the repository is advisable to avoid redundant memory usage and processing time.
  • Use Case 3 - User Authentication:
    • Singleton objects are beneficial in scenarios such as user authentication. For instance, in an app where multiple logins with the same credentials should be restricted for security reasons, a singleton object can ensure that only one instance of the user object exists.

Understanding Singleton Objects in Kotlin

Sample Android Program Demonstrating Singleton Object Usage

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