Kotlin classes, data classes, sealed classes, objects, companion objects, interfaces, delegation and extension functions.
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- What is the primary purpose of a data class in Kotlin?
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To hold data with automatically generated equals(), hashCode(), toString(), copy() and componentN() functions- How do you declare a data class in Kotlin?
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data class ClassName(val prop1: Type1, val prop2: Type2)- What does the copy() function do on a data class?
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Creates a shallow copy of the object, allowing you to modify specific properties in the new instance- What is a sealed class in Kotlin?
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A class that restricts which subclasses can inherit from it; all subclasses must be defined in the same file or nested- Why use a sealed class instead of an abstract class?
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Sealed classes provide exhaustive when expression checking, ensuring all subclass types are handled- How do you declare a singleton object in Kotlin?
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object SingletonName { ... }- What is the difference between object and class in Kotlin?
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object declares a singleton instance; class declares a template for creating multiple instances- What is a companion object in Kotlin?
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An object declared inside a class that can access private members and holds static-like properties and methods- How do you call a companion object member?
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ClassName.memberName (no instance needed, like static members in Java)- Can a class have more than one companion object?
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No, a class can have at most one companion object- How do you declare an interface in Kotlin?
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interface InterfaceName { fun method(): ReturnType; val property: Type }- Can Kotlin interfaces have properties?
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Yes, interfaces can have abstract properties and properties with default implementations- What is delegation in Kotlin?
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A design pattern where an object forwards method calls to another object, using the by keyword- How do you implement delegation in Kotlin?
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class Derived(val base: Base) : Base by base { ... }- What is an extension function in Kotlin?
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A function added to an existing class without inheritance or modification, using receiver.method() syntax
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