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Page 21 of 156
Why can't 'kotlin.Result' be used as a return type?
Result is a Serializable class in Kotlin. The function definition looks like this −class Result : SerializableThis class has two properties − "isFailure" and "isSuccess".As per the documentation, Result cannot be used as a direct return type of Kotlin function. However, in this article, we will see how we can use this Result in our Kotlin programs.// ERROR: 'kotlin.Result' cannot be used as a return type fun findUserByName(name: String): Result fun foo(): Result // ERROR fun foo(): Result? // ERROR var foo: Result // ERRORExample – Kotlin.Resultsealed class ...
Read MoreWhat's the difference between "!!" and "?" in Kotlin?
In this article, we will take an example and demonstrate the difference between (!!) and (?) in Kotlin.Example – "!!" and "?" operator in KotlinKotlin provides a wonderful operator to check NULL pointer exceptions. It throws a NULL pointer exception instead of breaking the programming logic whenever the variable is NULL.In the following example, the value of "test" is NULL. Hence, Kotlin will throw a NULL pointer exception instead of breaking down the logic. The example shows the different uses of "!!" and "?" operators.fun main(args: Array) { val nullValue: String ?=null // it will print null ...
Read MoreOverride getter for Kotlin data class
Data class is a collection in Kotlin to store data. Logically this is same as creating a Java POJO class. In Java, we do create extra member functions to set and get the data in the member variables. In Kotlin, we don’t need to create separate methods to access the member variables of the class. Kotlin provides it by default. We can access the variables by just using the member variable names in it.It is not recommended to override any of the data class members like we used to do in Java.It is always recommended to use normal class if ...
Read MoreWhat does 'by' keyword do in Kotlin?
Kotlin supports delegation of design pattern by introducing a new keyword "by". Using this keyword or delegation methodology, Kotlin allows the derived class to access all the implemented public methods of an interface through a specific object.ExampleIn this example, we will implement an abstract method of a Base class from another class.interface Base { //abstract method fun printMe() } class BaseImpl(val x: Int) : Base { // implementation of the method override fun printMe() { println(x) } } // delegating the public method on the object b class Derived(b: Base) : Base by b ...
Read MoreWhat is "out" keyword in Kotlin?
"Out" keyword is extensively used in Kotlin generics. Its signature looks like this −ListWhen a type parameter T of a class C is declared out, then C can safely be a super type of C. That means, a Number type List can contain double, integer type list.ExampleThe following example demonstrates how you can use the "out" keyword in Kotlin −fun main(args: Array) { var objet1 = genericsExample(10) var objet2 = genericsExample(10.0) } // As generic type is declared as "out", // we can pass Int and Double also. class genericsExample(input:Any?) { init { ...
Read MoreHow to read a text file from resources in Kotlin?
In this article, we will see how we can read a text file using Kotlin library functions. Kotlin is based on Java, hence we can use different Java library functions in Kotlin too.Example - BufferedReaderGo ahead and create a Kotlin file in your workspace and name it " ReadFile.kt". Keep a text file with some data in the same directory. For this example, our Text file looks like this −Welcome to the best tutorial website - www.tutorialsPoint.com This is the Text file that we want to read via KotlinExecute the following piece of code to read the above text file.// ...
Read MoreWhat does "?:" do in Kotlin? (Elvis Operator)
Elvis operator is very common in many programming languages. This is a binary expression that returns the first operand when the expression value is True and it returns the second operand when the expression value is False. Generally, the Elvis operator is denoted using "?:", the syntax looks like −First operand ?: Second operandExampleThe following example demonstrates how you can use the Elvis operator in Kotlin.fun main(args: Array) { val x: String? = null val y: String = x ?: "TutorialsPoint.com" // it will check whether the value of x ...
Read MoreWhen to use an inline function in Kotlin?
Kotlin is a statistically typed language. It has different options to handle higher-order functions. Kotlin came up with a wonderful solution for higher-order functions by introducing inline functions.An Inline function is a kind of function that is declared with the keyword "inline" just before the function declaration. Once a function is declared inline, the compiler does not allocate any memory for this function, instead the compiler copies the piece of code virtually at the calling place at runtime.You should opt for an inline function in Kotlin in the following situations −When you need to access higher-order functions.When you need to ...
Read MoreDifference between "*" and "Any" in Kotlin generics
In any programming language, generics are a powerful feature using which developers can create custom data type to manipulate a program in a different manner. There are many ways in which we can define generics in Kotlin.In this article, we will demonstrate the difference between "*" and "Any" keywords in Kotlin.When we define a collection with "*", it should contain the object of only that type. There should not be any mix and match between the data types inside a collection.If we use "Any", we can mix and match the data types, which means we can have multiple data types ...
Read MoreHow to check "instanceof" class in Kotlin?
Kotlin is a cross-platform, statistically typed, general-purpose programming language. It is very popular among the developer community because of its interoperable nature with JVM. In the programming world sometimes it is required to check the type of an object to implement a business logic.Unlike Java, we don't have an "instance of" operator in Kotlin. However, we have an "is" operator in Kotlin for type checking and casting.ExampleThe following example demonstrates how the "is" operator works in Kotlin.fun main(args: Array) { val x: String = "TutorialsPoint" // checking the instance and matching the type ...
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