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Tell me about the keyword Object in Kotlin and its application.

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Answer from AI

The keyword object in Kotlin is used for declaring:

  • Object Singletons (Object Declarations): Creates a single instance of a class, accessible globally. Initialized upon first access.
  • Companion Objects: Placed inside a class to declare static members (fields, methods). Allows access to them by class name without creating an instance.
  • Anonymous Objects (Object Expressions): Creates an instance of an anonymous class, often used for implementing interfaces or extending other classes "on the fly".
// Singleton example
object AppConfig {
    // singleton properties
    const val API_URL = "https://example.com/api/"
}

// Companion object example
class MyClass {
    // properties and methods of the companion object
    companion object {
        fun create(): MyClass {
            // initialization logic
            return MyClass()
        }
    }
}

// Example of using an anonymous object
interface ClickListener {
    // interface method
    fun onClick()
}

fun setupButton(listener: ClickListener) {
    // using an anonymous object
    val buttonClickListener = object : ClickListener {
        override fun onClick() {
            // method implementation
        }
    }
    listener.onClick() // calling the passed listener
}
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