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May 6, 2017 · Companion Object. A companion object is a specific type of object declaration that allows an object to act similar to static objects in other languages (such as Java). Adding companion to the object declaration allows for adding the "static" functionality to an object even though the actual static concept does not exist in Kotlin. Here's an ...
Jan 9, 2019 · Creat a lateinit Context field inside companion object. abstract class MyClass { companion object { private lateinit var context: Context fun setContext(con: Context) { context=con } } } And then set it after the app has started
Oct 19, 2017 · The kotlin companion object provides an alternative (and with advantages) to the static for situations where class attributes are accessed without an object instance (like factories), but there is another use of static for cases where although an object instance may be available, a static is appropriate since a single attribute can be shared by all members of the class and the attribute is not instance dependant.
First, Kotlin doesn't use the Java concept of static members because Kotlin has its own concept of objects for describing properties and functions connected with singleton state, and Java static part of a class can be elegantly expressed in terms of singleton: it's a singleton object that can be called by the class' name. Hence the naming: it's an object that comes with a class.
May 18, 2017 · Kotlin properties declared in a named object or a companion object will have static backing fields either in that named object or in the class containing the companion object. Usually these fields are private but they can be exposed in one of the following ways: @JvmField annotation; lateinit modifier; const modifier.
When switching to Kotlin, static methods are moved into a companion object. However, there is no obvious way to unit test other methods which call these "static method". In Java, we could use PowerMockito's MockStatic(SomeClass.class) to verify a static method is called in the method under test.
Jun 1, 2018 · The same applies for objects, including companion objects. companion just lets you refer to this object as Person1 in addition to Person1.myc. Your fun constructor isn't a constructor; it's just a method called constructor.
Dec 13, 2019 · Yes, companion object is Kotlin's equivalent of static members in Java. Everything that applies to static, applies to companion object as well. The use of companion object depends on how it interacts with the state of class's object.
Feb 14, 2018 · Because Kotlin, for the fields in a companion object, creates a private field in the Companion class, and wraps it with getter/setter. But your Java code or library needs a real static field in the class. (Some Java libraries may support Kotlin's Companion, though). Therefore, Kotlin comes with these two:
Nov 2, 2017 · Generic type parameters of the class are not allowed inside the companion objects. The reason is that a single companion object is shared across all the instances of that class. This is true also for the different parameterized types of the same class. So, for example, the companion object is the same for whether it is a Foo<String> or a Foo<Int>.
