Kotlin

Kotlin is a cross-platform, statically typed, general-purpose programming language with type inference. So if you are having an interview in coming days, then you must checkout these question and answers which guide you further to ace the job interview.

Q.1 What are data classes in Kotlin, and how are they different from regular classes?

Data classes are classes specifically designed to hold data, and they automatically generate useful methods like toString(), equals(), and hashCode().

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Q.2 What are type inference and type annotations in Kotlin?

Type inference allows the compiler to automatically determine the data type of a variable, while type annotations explicitly specify the data type.

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Q.3 Explain the difference between rangeTo() and downTo() in Kotlin.

rangeTo() creates a range from a smaller value to a larger value, while downTo() creates a range from a larger value to a smaller value.

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Q.4 What is a higher-order function, and how do you define one in Kotlin?

A higher-order function is a function that takes one or more functions as parameters or returns a function. You define one by specifying functions as parameters or return types.

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Q.5 What are default arguments in Kotlin functions, and how do you use them?

Default arguments allow you to specify default values for function parameters, making it optional to provide values when calling the function. You declare default arguments in the function declaration.

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Q.6 What is the infix keyword in Kotlin, and how do you use it?

The infix keyword allows you to call a function using infix notation by placing it between the receiver and the argument. You define an infix function using the infix modifier.

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Q.7 How do you declare a lambda function in Kotlin?

Lambdas are declared with a set of parentheses for parameters, followed by -> and the lambda body. For example: (x: Int, y: Int) -> x + y.

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Q.8 What is the purpose of the with function in Kotlin?

The with function allows you to operate on an object within a specific context, reducing the need to repeat the object's name.

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Q.9 How does Kotlin handle null safety?

Kotlin uses a combination of nullable types and non-nullable types to enforce null safety, reducing the likelihood of null pointer exceptions.

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Q.10 What is the safe call operator (?.) in Kotlin, and when should you use it?

The safe call operator allows you to safely access properties or call methods on nullable objects. It returns null if the object is null. You should use it when working with nullable types.

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Q.11 Explain the use of the safe cast operator (as?) in Kotlin.

The safe cast operator attempts to cast an object to a specified type and returns null if the cast is unsuccessful. It's used for type-safe casting.

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Q.12 What is smart casting in Kotlin, and how does it work?

Smart casting is a feature that automatically casts a variable to a non-nullable type after checking it for null, simplifying code when working with nullable types.

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Q.13 What are extension functions in Kotlin, and why are they useful?

Extension functions allow you to add new functions to existing classes without modifying their source code, making it easy to extend built-in or third-party classes.

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Q.14 What are the benefits of using Kotlin's extension functions?

Benefits include code readability, improved API design, and the ability to add functionality to classes without altering their source code.

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Q.15 How does Kotlin handle primitive types and wrapper types?

Kotlin automatically converts between primitive types and their wrapper types (e.g., Int and Integer) when needed, providing a seamless experience.

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Q.16 What is the when expression in Kotlin, and how is it used?

The when expression is similar to a switch statement in other languages, allowing you to branch code based on the value of an expression or multiple conditions.

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Q.17 How do you use when expressions for pattern matching in Kotlin?

You can use when expressions with patterns, such as specifying values, ranges, or types, to match conditions and execute code accordingly.

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Q.18 What is the purpose of the break and continue labels in Kotlin?

Labels in Kotlin are used with break and continue statements to specify which loop they should affect when nested loops are present.

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Q.19 Explain the use of the for loop in Kotlin.

The for loop in Kotlin is used to iterate over a range, a collection, or any iterable object, making it easy to perform repetitive tasks.

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Q.20 What are ranges in Kotlin, and how are they useful?

Ranges represent a sequence of values between a start and an end, and they are useful for looping, comparisons, and other operations.

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Q.21 How do you specify the data type of a variable in Kotlin?

You can specify the data type of a variable explicitly using type annotations, such as val x: Int = 10, or rely on type inference.

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Q.22 What is the primary constructor in Kotlin, and how is it declared?

The primary constructor is declared in the class header and is responsible for initializing the class properties. It can include constructor parameters.

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Q.23 What are secondary constructors in Kotlin, and how are they declared?

Secondary constructors are additional constructors in a class that are defined using the constructor keyword inside the class body.

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Q.24 What is a named argument in Kotlin, and how do you use it?

A named argument allows you to specify function parameters by name when calling a function, improving code readability. For example, foo(arg2 = 42, arg1 = "hello").

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Q.25 How does Kotlin handle function overloading?

Kotlin allows function overloading, where you can define multiple functions with the same name but different parameter lists. The appropriate function is called based on the arguments provided.

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Q.26 What is the purpose of the apply function in Kotlin?

The apply function is used to configure an object and apply a block of code to it. It returns the modified object, making it useful for building and initializing objects.

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Q.27 Explain the also function in Kotlin and its use cases.

The also function is similar to apply but returns the original object. It is often used for side effects or logging during object configuration.

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Q.28 How do you create and work with sets in Kotlin?

Sets are created using the setOf, mutableSetOf, or HashSet constructors, and they store unique elements. You can add, remove, and iterate over set elements.

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Q.29 What is the lazy function in Kotlin, and how is it used?

The lazy function is used to create properties that are computed only when accessed for the first time, improving performance by delaying initialization.

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Q.30 Explain the purpose of the withIndex function in Kotlin.

The withIndex function is used to iterate over a collection along with its index, making it easy to access both the element and its position.

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Q.31 How do you declare and use single-line comments in Kotlin?

Single-line comments in Kotlin are denoted by //, and they are used to add explanatory notes or comments to the code.

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Q.32 What is the difference between /* */ and // comments in Kotlin?

/* */ comments are used for multi-line comments, while // comments are used for single-line comments.

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Q.33 Explain the concept of object expressions in Kotlin.

Object expressions allow you to create anonymous objects with a specified type or supertype, often used for ad-hoc implementations of interfaces or classes.

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Q.34 What is the purpose of the is operator in Kotlin?

The is operator is used to check the type of an object and perform type-safe casting. It's similar to the instanceof operator in other languages.

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Q.35 How do you handle exceptions in Kotlin?

Exceptions are handled using try-catch blocks. Kotlin has concise syntax for catching exceptions and provides the try expression for handling exceptions as an expression.

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Q.36 What is the throw expression in Kotlin, and how is it used?

The throw expression is used to explicitly throw an exception. You specify the exception type and an optional message.

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Q.37 Explain the use of the use function in Kotlin.

The use function is used to work with resources (e.g., files, streams) that need to be closed after use. It ensures proper resource management by closing the resource when the code block exits.

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Q.38 What is the purpose of the break and continue statements in Kotlin loops?

break is used to exit a loop prematurely, while continue is used to skip the current iteration and proceed to the next one.

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Q.39 How do you work with files and input/output in Kotlin?

Kotlin provides various classes and functions for working with files and input/output operations, including reading and writing files, handling exceptions, and managing resources.

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Q.40 What is a type alias in Kotlin, and how is it declared?

A type alias allows you to define custom names for existing types, improving code readability. It's declared using the typealias keyword.

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Q.41 What is the Kotlin Android Extensions plugin, and how is it used?

Kotlin Android Extensions is a plugin that simplifies Android development by allowing you to access views in XML layouts as properties in your Kotlin code.

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Q.42 Explain the concept of destructuring declarations in Kotlin.

Destructuring declarations allow you to extract the components of data structures like pairs or custom objects into separate variables, improving code readability.

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Q.43 How do you define a package in Kotlin, and what is its purpose?

You define a package using the package keyword, and it is used to organize and group related classes and functions in a hierarchical structure.

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Q.44 What is the reified modifier in Kotlin, and when is it used?

The reified modifier is used with inline functions to access type information at runtime. It is often used in conjunction with the is operator and type checks.

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Q.45 Explain the purpose of the infix modifier in Kotlin, and when is it used?

The infix modifier allows you to call functions using infix notation by placing the function name between the receiver and the argument, improving code readability.

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Q.46 What are extension properties in Kotlin?

Extension properties allow you to add new properties to existing classes without modifying their source code, enhancing their functionality.

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Q.47 How do you declare an extension property in Kotlin?

Extension properties are declared by prefixing the property name with the receiver type and using the . operator.

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Q.48 What are labeled expressions and how are they used in Kotlin?

Labeled expressions allow you to label code blocks and use labels with return, break, and continue statements, providing more control over program flow.

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Q.49 Explain the equals() function in Kotlin, and how does it differ from ==?

The equals() function is used to compare the content of two objects for structural equality, while == is used for reference equality.

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Q.50 How does Kotlin handle default arguments in function calls?

Kotlin allows you to specify default values for function parameters, making it optional to provide values when calling the function.

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Q.51 What is a lambda expression in Kotlin, and how is it declared?

A lambda expression is an anonymous function that can be used as a variable, argument, or return value. They are defined using the {} or -> syntax.

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Q.52 Explain the with function in Kotlin, and when is it commonly used?

The with function is used to operate on an object within a specific context, reducing the need to repeat the object's name. It is commonly used for configuring objects or invoking multiple methods on the same object.

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Q.53 What is type inference in Kotlin, and how does it work?

Type inference is a feature that allows the Kotlin compiler to automatically determine the data type of a variable based on its value and usage, reducing the need for explicit type declarations.

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Q.54 How do you define a named argument in Kotlin function calls, and when is it useful?

Named arguments allow you to specify function parameters by name when calling a function, improving code readability and making it clear which arguments correspond to which parameters.

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Q.55 What is the purpose of the lateinit modifier in Kotlin, and when is it used?

The lateinit modifier is used to declare non-null properties that are initialized later, typically in the class's constructor or an init block. It is useful for properties that cannot be initialized during object creation.

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Q.56 Explain the concept of object expressions in Kotlin, and when are they typically used?

Object expressions allow you to create anonymous objects with a specified type or supertype, often used for ad-hoc implementations of interfaces or classes, or for encapsulating small pieces of behavior.

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Q.57 What is the difference between rangeTo() and downTo() in Kotlin, and when are they used?

rangeTo() creates a range from a smaller value to a larger value, while downTo() creates a range from a larger value to a smaller value. They are used in loops, comparisons, and other operations involving ranges of values.

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Q.58 How do you create and work with maps in Kotlin?

Maps are created using the mapOf, mutableMapOf, or HashMap constructors, and they store key-value pairs. You can add, remove, and access values using keys.

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Q.59 Explain the apply function in Kotlin, and what are its common use cases?

The apply function is used to configure an object and apply a block of code to it. It returns the modified object, making it useful for building and initializing objects with a fluent and concise syntax.

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Q.60 What is the purpose of the also function in Kotlin, and how is it used?

The also function is similar to apply but returns the original object. It is often used for performing side effects, such as logging or additional actions, during object configuration.

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Q.61 How do you work with arrays in Kotlin, and what are the different ways to create arrays?

Arrays in Kotlin can be created using the arrayOf, intArrayOf, charArrayOf, and other array constructors. You can access, modify, and iterate over array elements.

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Q.62 What is the when expression in Kotlin, and how is it used for pattern matching?

The when expression is used for branching code based on the value of an expression or multiple conditions. It can be used for pattern matching by specifying patterns, values, or types to match against.

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Q.63 How do you handle exceptions in Kotlin, and what is the syntax for catching exceptions?

Exceptions are handled using try-catch blocks in Kotlin. The try keyword is followed by a block of code where exceptions may occur, and catch blocks specify exception types and code to handle them.

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Q.64 What is the purpose of the break and continue statements in Kotlin loops, and how do they differ?

The break statement is used to exit a loop prematurely, while the continue statement skips the current iteration and proceeds to the next one. They control the flow of loop execution.

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Q.65 What is Kotlin?

Kotlin is a statically-typed, modern programming language that runs on the Java Virtual Machine (JVM). It's concise, expressive, and designed to improve developer productivity.

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Q.66 How is Kotlin different from Java?

Kotlin offers concise syntax, null safety, extension functions, and many modern features that make it more expressive and less error-prone compared to Java.

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Q.67 What are the key features of Kotlin?

Key features include null safety, extension functions, smart casts, data classes, coroutines, and seamless Java interoperability.

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Q.68 What is null safety in Kotlin?

Null safety in Kotlin ensures that null values are handled safely, reducing the likelihood of null pointer exceptions.

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Q.69 How do you declare a variable in Kotlin?

Variables are declared using the val keyword for read-only (immutable) variables and var for mutable variables.

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Q.70 What is the difference between val and var in Kotlin?

val declares read-only (immutable) variables, while var declares mutable variables that can be reassigned.

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Q.71 How do you define a function in Kotlin?

Functions are defined using the fun keyword, followed by the function name, parameters, and return type.

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Q.72 What is type inference in Kotlin?

Kotlin's type inference system allows you to omit explicit type declarations when the type can be inferred from the context.

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Q.73 How do you create a Kotlin class?

You use the class keyword followed by the class name and an optional constructor to create a class in Kotlin.

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Q.74 Explain the primary constructor and secondary constructors in Kotlin.

The primary constructor is defined in the class header, while secondary constructors are defined using the constructor keyword within the class body.

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Q.75 What are data classes in Kotlin?

Data classes are classes specifically designed to hold data, automatically generating useful methods like toString(), equals(), and hashCode().

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Q.76 How do you create an instance of a class in Kotlin?

You create an instance of a class using the val or var keyword followed by the class constructor.

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Q.77 What are default arguments in Kotlin?

Default arguments allow you to specify default values for function parameters, making it optional to provide values when calling the function.

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Q.78 How do you handle nullable types in Kotlin?

You use the ? operator to declare nullable types, allowing variables to hold either non-null values or null.

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Q.79 What is the Elvis operator in Kotlin?

The Elvis operator (?:) is used to provide a default value when an expression results in null.

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Q.80 Explain Kotlin's when expression.

The when expression is similar to a switch statement in other languages and allows you to branch code based on the value of an expression.

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Q.81 How do you define the Target Platform of Kotlin and how is Kotlin-Java interoperability possible?

Java Virtual Machine(JVM) is the Target Platform of Kotlin. Such that Kotlin is 100% interoperable with Java since both, on compilation produce bytecode. Therefore Kotlin code can be referred from Java and vice-versa.

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Q.82 What is a lambda expression in Kotlin?

A lambda expression is an anonymous function that can be used as a variable, argument, or return value. They are defined using the {} or -> syntax.

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Q.83 Differentiate between const and a val?

Some of the points of difference between const and val are -
1. By default val properties are set at runtime. Therefore by adding a const modifier on a val would make a compile-time constant.
2.A const cannot be used with a var or on its own.
3 A const is not applicable on a local variable.

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Q.84 How do you declare a lambda in Kotlin?

Lambdas are declared with a set of parentheses for parameters, followed by -> and the lambda body. For example: (x: Int, y: Int) -> x + y

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Q.85 Does Kotlin permit the use of primitive types like int, float, double?

Kotlin does not permit the use of primitive types like int, float, double at the language level. The JVM bytecode that’s compiled does certainly have them.

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Q.86 What is a higher-order function in Kotlin?

A higher-order function is a function that takes one or more functions as parameters or returns a function. Kotlin supports them natively.

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Q.87 What is the entry point of every Kotlin Program?

The primary function is the entry point of every Kotlin program. Such that in Kotlin we can choose not to write the main function inside the class. Thereby on compiling the JVM implicitly encapsulates it in a class. Also the strings passed in the form of Array are used to retrieve the command line arguments.

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Q.88 What is an extension function in Kotlin?

An extension function allows you to add new functions to existing classes without modifying their source code.

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Q.89 Differentiate between == and === operators in Kotlin?

== is used to compare the values are equal or not. On the other hand === is used to check if the references are equal or not.

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Q.90 How do you define an extension function in Kotlin?

Extension functions are defined by prefixing the function name with the receiver type and using the . operator.

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Q.91 What are the visibility modifiers available in Kotlin and what is the default visibility modifier?

Some of the visibility modifiers available in Kotlin are - public, internal, protected, and private. Also 'public' is the default visibility modifier.

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Q.92 What is a nullable receiver in extension functions?

A nullable receiver allows you to define extension functions on nullable types, providing additional functionality when the receiver is not null.

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Q.93 Name the types of constructors in Kotlin?

Mainly constructors in Kotlin are of two types namely -
1. Primary constructors – These are defined in the class headers. Such that they cannot hold any logic. There’s only one primary constructor per class.
2. Secondary constructors – They are defined in the class body. They must delegate to the primary constructor if it exists. They can hold logic. There can be more than one secondary constructors.

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Q.94 What is smart casting in Kotlin?

Smart casting is a feature that automatically casts a variable to a non-nullable type after checking it for null.

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Q.95 How do you define 'init block' in Kotlin?

init is the initialiser block in Kotlin which is executed once the primary constructor is instantiated. Such that if you invoke a secondary constructor, then it works after the primary one as it is composed in the chain.

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Q.96 What are Kotlin collections?

Kotlin provides a rich set of collection types, including lists, sets, and maps, with functional operations like map, filter, and reduce.

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Q.97 Name the different type of arguments inside a constructor?

The constructor arguments are val unless explicitly set to var.

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Q.98 How do you iterate through a collection in Kotlin?

You can use for loops or functional methods like forEach to iterate through collections in Kotlin.

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Q.99 Differentiate between lazy and lateinit.

The points of difference between lazy and lateinit are -
1. Both are used to delay the property initializations in Kotlin
On one hand lateinit is a modifier used with var and is used to set the value to the var at a later point whereas lazy is a method or rather say lambda expression. It’s set on a val only. The val would be created at runtime when it’s required

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Q.100 What is the let function in Kotlin?

The let function is used to safely perform operations on nullable objects, and it only executes the lambda if the object is not null.

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Q.101 What are the advantages of using Kotlin?

The advantages of using Kotlin are -
1. Kotlin language is easy to learn as its syntax is similar to Java.
2. Kotlin is a functional language and based on JVM. So, it removes lots of boiler plate
3.It is an expressive language which makes code readable and understandable.

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Q.102 What are Kotlin Android Extensions?

Kotlin Android Extensions is a plugin that allows you to access views in Android XML layouts as properties in your Kotlin code.

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Q.103 How do you define ‘Null Safety’ in Kotlin?

In Kotlin, Null Safety feature permits to remove the risk of occurrence of NullPointerException in real time. Such that it is also possible to differentiate between nullable references and non-nullable references.

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Q.104 What is the safe call operator (?.) in Kotlin?

The safe call operator allows you to safely access properties or call methods on nullable objects. If the object is null, it returns null.

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Q.105 Why is Kotlin interoperable with Java?

The reason for Kotlin to interoperable with Java is sine it uses JVM bytecode. Therefore the process of compiling it directly to bytecode helps to achieve faster compile time and makes no difference between Java and Kotlin for JVM.

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Q.106 What is the safe cast operator (as?) in Kotlin?

The safe cast operator attempts to cast an object to a specified type and returns null if the cast is unsuccessful.

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Q.107 What are the extension methods Kotlin provides to java.io.File?

The extension methods Kotlin provides to java.io.File are -
1. bufferedReader(): Use for reading contents of a file into BufferedReader
2. readBytes() : Use for reading contents of file to ByteArray
3. readText(): Use of reading contents of file to a single String
4. forEachLine() : Use for reading a file line by line in Kotlin
5. readLines(): Use to reading lines in file to List

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Q.108 How do you define a nullable type in Kotlin?

You declare a nullable type by adding ? to the end of the type, such as String? to indicate a nullable string.

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Q.109 What is the default behavior of Kotlin classes?

In Kotlin all classes are final by default since Kotlin permits multiple inheritances for classes, and an open class is more expensive than a final class.

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Q.110 What is the purpose of the lateinit modifier in Kotlin?

The lateinit modifier allows you to declare non-null variables that are initialized later, typically in the class's constructor or an init block.

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Q.111 Does Kotlin offer any additional functionality for standard Java packages or classes?

Kotlin programs can easily run on standard JVM like any another compiled Java code. It permits JVM to compile any program to byte-code. Kotlin is accessible using Java Virtual Machine. Therefore, Kotlin is almost similar to Java. Also Kotlin applications can be built with parts of Java code.

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Q.112 How do you create a singleton in Kotlin?

You can create a singleton by using the object keyword followed by the singleton name, and it will be lazily initialized.

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Q.113 Define the use of abstraction in Kotlin.

Abstraction is defined as one of the most important concept of Objected Oriented Programming. In Kotlin, abstraction class is used when you know the functionalities a class should have. One may not be aware of how the functionality is implemented or if the functionality can be implemented using different methods.

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Q.114 What is a sealed class in Kotlin?

A sealed class is a class that restricts its subclasses to a finite set of known classes, often used in when expressions for exhaustive checks.

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Q.115 Describe the default behavior of Kotlin classes?

All classes are final by default, in Kotlin because Kotlin allows multiple inheritances for classes, and an open class is more expensive than a final class.

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Q.116 Explain the init block in Kotlin.

The init block is used to initialize properties or perform initialization logic when an instance of a class is created.

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Q.117 Describe the features that are there in Kotlin but not In Java.

Some of the important Kotlin features that Java does not have -
1. Null Safety
2. Operator Overloading
3. Coroutines
4. Range expressions
5. Smart casts
6. Companion Objects

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Q.118 What is the Elvis operator (?:) in Kotlin?

The Elvis operator provides a concise way to provide a default value if an expression results in null. It's used as expression ?: defaultValue.

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Q.119 What are Higher-Order Functions?

Higher-Order Functions can be defined as a function that takes functions as parameters, or returns a function.

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Q.120 How do you declare a constant in Kotlin?

You declare a constant using the const modifier for top-level or object-level properties, and they must be of a primitive or string type.

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Q.121 Name the different types of strings available in Kotlin and what do you understand by Kotlin String Interpolation?

The different types of strings available in Kotlin are -
1. Strings are a collection of characters together. Such that Kotlin features two types of strings, and they are - Raw string and Escaped string
In Kotlin String, templates can be evaluated. This evaluation of string templates is referred as the string template interpolation.

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Q.122 What is the difference between val and const val in Kotlin?

val is a read-only property, while const val declares a compile-time constant that must be initialized with a constant value.

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Q.123 Explain type aliases in Kotlin.

Type aliases allow you to define custom names for existing types, making code more readable and expressive.

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Q.124 How do you work with nullable types in Kotlin?

You can use safe calls (?.), the Elvis operator (?:), or the safe cast operator (as?) to work with nullable types safely.

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Q.125 What is the Kotlin Standard Library?

The Kotlin Standard Library provides a wide range of useful functions and extension functions to simplify common programming tasks.

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Q.126 How do you create an instance of an enum class in Kotlin?

You create an instance of an enum class by specifying one of its enum constants, such as MyEnum.VALUE.

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