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Learn how to create and use companion objects in Kotlin, which are similar to static methods in Java. See examples of how to access private members and implement factory methods with companion objects.
- Overview
- Declare A Companion Object
- Named Companion Object
- Inheritance and Companion Object
- Java Interoperability
- Interfaces and Companion Object
- Conclusion
There are times we need to use a companion object to define class members that are going to be used independently of any instance of that class.The Kotlin compiler guarantees we will have one and only one instance of a companion object. For those of us with a background in Java and C#, a companion object is similar to static declarations. As an ill...
Here is the syntax of defining a companion object: Now, properties and functions defined within the companion object body are accessible by referring to the class name: Moreover, it’s possible to use them inside the class without the class name: When we utilize one of the companion object members, it will be initialized. Besides that, a companion o...
By default, a companion object’s name is Companion. However, it is possible to rename it. Let’s implement a Factory Method design pattern in its simplest form. The Factory Method design pattern handles object creation. We’ll implement this design pattern using a companion object. Let’s name its companion object Factory: Now, if we prefer to make us...
A companion object is not inheritable. But it can inherit from another class or implement interfaces.This is one of the reasons that a companion object is similar to static declarations in Java and C#. Let’s look at another simple example that benefits from companion object inheritance to implement the Abstract Factory design pattern. Conceptually,...
As we know, a companion object can inherit a class or interfaces — something that is not viable in Java static members.So, if we need a Java-interoperable code, the solution is @JvmStatic functions and @JvmStatic properties. By annotating a companion object’s members with @JvmStatic, we will gain better Java interoperability: Access Kotlin Companio...
A companion object can be used in interfaces as well.We can define properties and concrete functions within a companion object enclosed in an interface. One potential usage is storing constants and helper functions related to the interface:
In this article, we looked at the details of a companion object. It’s a place to share functions and properties with all class instances. As always, code samples are available over on GitHub.
May 6, 2020 · In short, companion objects are singleton objects whose properties and functions are tied to a class but not to the instance of that class — basically like the “static” keyword in Java but with...
Jun 8, 2022 · There is a way to call a static method as you would do in Java. To achieve this, you will have to place your object within a class and mark it as a companion object. This concept of a companion object will be familiar to someone with at least entry-level knowledge of Scala.
4 days ago · Companion objects allow you to define class-level functions and properties tied to a class, simplifying the creation and management of these instances. Modifying existing class behavior temporarily: You want to modify the behavior of an existing class without the need to create a new subclass.
Sep 2, 2019 · In Kotlin, if you want to write a function or any member of the class that can be called without having the instance of the class then you can write the same as a member of a companion object inside the class.
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Dec 16, 2023 · Learn how to use companion objects, a special object bound to a class definition, to replace static methods and fields in Kotlin. See examples of how to access private members, implement interfaces, and cache values with companion objects.
