The only difference is that we don’t specify the value for it since it will only be mapped by that. Val user3 = User("Dave", 34, givenList_whenConvertToMap_thenResult(). arrayListOf - Kotlin Programming Language Common JVM JS Native Version 1.8 kotlin-stdlib / llections / arrayListOf arrayListOf Common JVM JS Native 1. The ArrayList class in Kotlin can be used to create a variable of ArrayList type. Val user2 = User("Sara", 25, listOf("Chess")) So, it explains how the reassignment happens.įurther, let’s look at the implementation of List‘s ‘ +‘ ( plus operation) operator: public operator fun Collection.Kotlin offers the convenient toMap method which, given a list of complex objects, will allow us to have elements in our list mapped by any values we provide: val user1 = User("John", 18, listOf("Hiking")) Now, let’s take a closer look at this compilation error. First, as the List interface and its super types don’t have the plusAssign() function, here, myList += “Tom Cruise” is the same as myList = myList + “Tom Cruise”. However, the error message is different this time: “ Kotlin: Val cannot be reassigned.” Next, let’s test the += operator: val myList = listOf("Tom Hanks", "Brad Pitt")Īs we’ve expected, the code doesn’t compile either. If we compile the code above, the compiler complains: “Kotlin: Unresolved reference: add.” This is expected, as the List interface doesn’t have the add() method. The sort() method modifies the list in-place, and a sorted() built-in. Use map.keys and map.values to get the all keys and values. import .kotlin.readValue val listOfD: List jacksonMapper.readValue(jsonStr). Next, adding few key value pairs to the map. First create the HashMap object with HashMap () constructor.
But let’s create a test to verify if it’s true: var myList = listOf("Tom Hanks", "Brad Pitt") Converting HashMap to List in Kotlin Using ArrayList Constructor This approach is the simple one and easy. FileUtils is returning a LinkedList and that is why you are having issues. Since List is read-only, we can’t add an element to it. ArrayList is a class with implementation details. Finally, let’s look at the List type in Kotlin.
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