Retrieve Single Elements In Kotlin
Last Updated :
21 Oct, 2021
Kotlin Collections allows to retrieve single elements with respect to different conditions. It totally depends on what kind of Collection is used to store the data. The elements of a collection can be retrieved by position, condition, randomization and with respect to the existence of that element in the list.
Retrieving by Position –
elementAt(index): – elementAt() takes index of the element and retrieve it from the list. The index of the list starts from 0 and goes till n-1 where n is no of elements within the list. It is the most simple and easiest way to retrieve the element and is only preferred when the position of the needed element is known in advance.
Kotlin program of using elementAt() method –
Java
fun main(args: Array<String>) {
val list=listOf("GeeksforGeeks","A","Computer","Science","Portal")
println(list.elementAt(0))
}
|
Output:
GeeksforGeeks
There are number of method used to retrieve an element from the list but to avoid exception when retrieving non-existing elements we should use safe methods. Two of the methods are:
elementAtOrElse(index){lambda expression}: – It is an addition over elementAt() and executes lambda expression when the index is not found.
elementAtOrNull(index): – It is an addition over elementAt() and returns null when the index is not found.
Kotlin program of retrieving element using safe cast –
Java
fun main(args: Array<String>) {
val list=listOf("GeeksforGeeks","A","Computer","Science","Portal")
println(list.elementAtOrNull(5))
println(list.elementAtOrElse(5){"Element index not found"})
}
|
Output:
null
Element index not found
We can also retrieve first and last element from the list below two methods –
first(): – It is used to retrieve the first element from the list i.e having the index 0.
last(): – It is used to retrieve the last element of the list i.e having the index n-1 where n is the size of the list.
Kotlin program of using first() and last() methods –
Java
fun main(args: Array<String>) {
val list=listOf("GeeksforGeeks","A","Computer","Science","Portal")
println(list.first())
println(list.last())
}
|
Output:
GeeksforGeeks
Portal
Retrieving by condition –
Using first() and last() method, we can retrieve the elements matching a given predicate.
Java
fun main(args: Array<String>) {
val numbers = listOf("Geeks","for","Geek","A","Computer","Science","Portal")
println(numbers.first { it.length > 5 })
println(numbers.last { it.startsWith("G") })
}
|
Output:
Computer
Geek
Both functions throw exceptions, if no elements found matching the predicate. To avoid exception, we use firstOrNull() and lastOrNull() and they will return null if no matching elements are found.
Java
fun main(args: Array<String>) {
val numbers = listOf("Geeks","for","Geek","A","Computer","Science","Portal")
println(numbers.firstOrNull { it.length > 9 })
println(numbers.lastOrNull { it.startsWith("B") })
}
|
Output:
null
null
Random Retrieving –
If we want to retrieve an arbitrary element from the list we can use random() function.
random(): – It returns a random element from the collection.
Example: –
Java
fun main(args: Array<String>) {
val strings = listOf("Geeks","for","Geek","A","Computer","Science","Portal")
println(strings.random())
}
|
Output:
Computer (output can be same or different)
Checking existence –
contains(element): –It is used to check if an element is in the list or not. It returns true if element is there else it returns false.
containsAll(elements[]): – It is used to check if all the elements are in the list or not. It returns true if all the elements are there else it returns false.
in keyword: – It is used to check if all the elements are in the list or not. It returns true if the element are there else it returns false.
isEmpty(): – It is used to check if the list is empty or not. It returns true if the elements are not in list else it returns false.
isNotEmpty(): – It is used to check if the list is empty or not. It returns true if the elements are in list else it returns false.
Kotlin program of checking existence of string in a list –
Java
fun main(args: Array<String>) {
val list=listOf("Geeks","for","Geek","A","Computer","Science","Portal")
println(list.contains("For"))
println(list.containsAll(listOf("A", "Computer")))
println(list.isEmpty())
println(list.isNotEmpty())
}
|
Output:
false
true
false
true
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