Several common applications of Kotlin List and Java List

List in Kotlin

List collections in Kotlin are mainly divided into mutable and immutable

Type 1: immutable

1. Create an empty List collection, which is not common, because it is immutable (only readable) and an empty collection;

val lse:List<String> =  listOf<String>()

2. Create a non-empty List collection

val lsn:List<String> = listOf<String>("a","java","C++","Kotlin") println(lsn)

printout

[a, java, C++, Kotlin]

The second type: variable

1. Create a controllable List collection

val ml = mutableListOf<String>()//创建一个空List集合 
ml.add("cc") 
ml.add("dd") 
ml.add("ee") 
ml.add("ff") 
println(ml)

printout

[cc, dd, ee, ff]

Create a non-empty mutable List collection

val mln = mutableListOf<String>("cc","dd","ee") 
mln.add("ff") 
println(mln)

printout

[cc, dd, ee, ff]

MutableList inline function passes a List

Defined in Collections.kt

public inline fun <T> MutableList(size: Int, init: (index: Int) -> T): MutableList<T> {

}

var ls = MutableList<String>(5) {//创建一个默认有5个元素的可变集合 
    "java$it"//默认元素的值 
} 
ls.add("apple") 
ls.add("sss") 
ls.add("aaa") 
ls.add("bbb") 
println(ls)

output

 [java0, java1, java2, java3, java4, apple, sss, aaa, bbb]

Using Java List in Kotlin

Kotlin can also use List in Java

Java writing method, directly calling Java API

private var listTask: ArrayList<String> = ArrayList<String>()

Kotlin also provides an API to create a List collection in Java

private var ls:ArrayList<String> = arrayListOf<String>()

In other words, using Java List in Kotlin is a Java way of writing, first create a List collection object, and then add elements; but it is also an ArrayList object in Java created;