【Kotlin】集合Iterable/Collection/List/Set/Map
出處 : https://blog.csdn.net/vitaviva/article/details/107587134
建立集合
不可變更集合 immutable
import java.util.*
import java.text.SimpleDateFormat
/**
* You can edit, run, and share this code.
* play.kotlinlang.org
*/
fun main() {
val list = listOf(1,2,3, null)
// 不為 null List
val notNullList = listOfNotNull(null,1,2,3,null)
val emptyList = emptyList<Int>()
val map = mapOf("foo" to "FOO", "bar" to "BAR", "bar" to "BB")
val set = setOf(4,5,6,6)
println(list) // [1, 2, 3, null]
println(notNullList) // [1, 2, 3]
println(emptyList) // []
println(map) // {foo=FOO, bar=BB}
println(set) // [4, 5, 6]
}
可變更集合 mutable
import java.util.*
import java.text.SimpleDateFormat
/**
* You can edit, run, and share this code.
* play.kotlinlang.org
*/
fun main() {
val list = mutableListOf(1,2,3,3)
val map = mutableMapOf("foo" to "FOO", "bar" to "BAR", "bar" to "BB")
val set = mutableSetOf(1,2,3,3)
println(list) // [1, 2, 3, 3]
println(map) // {foo=FOO, bar=BB}
println(set) // [1, 2, 3]
}
addAll(), list 相加
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val list1 = mutableListOf(1,2,3,4)
val list2 = mutableListOf(5,6,7,8)
println(list1.addAll(list2)) // true (注意當下有返回值)
println(list1) // [1, 2, 3, 4, 5, 6, 7, 8
}
remove(), list 刪除
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val numberList = mutableListOf(1,2,3)
numberList.remove(2)
println(numberList) // [1, 3]
}
索引
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val list = listOf(1,2,3)
val indices: IntRange = list.indices
println(indices)
for(i in list.indices){
println(list[i])
}
/*
0..2
1
2
3
*/
println(list.first()) // 1
println(list.last()) // 3
println(list.lastIndex) // 2 = ( size - 1 )
println(list.size) // 3
}Stream 與 kotlin 比較
List 相關
list.map{}
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val nameList = listOf("Sam","John",null,"Mary")
val resultList = nameList.map{ "name:" + it }
println(resultList) // [name:Sam, name:John, name:null, name:Mary]
// 過濾null
val resultList2 = nameList.mapNotNull{ it }
println(resultList2) // [Sam, John, Mary]
}
list 保留或排除(removeAll(), retainAll())
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val peopleList = mutableListOf(People("sam",18),People("John",23),People("Mary",30))
// 移除 age > 25
peopleList.removeAll{ it.age > 25 } // [People(name=sam, age=18), People(name=John, age=23)]
println(peopleList)
// 保留 name == sam
val peopleList2 = mutableListOf(People("sam",18),People("John",23),People("Mary",30))
peopleList2.retainAll{ it.name == "sam" } // [People(name=sam, age=18)]
println(peopleList2)
}
list 轉 map
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val peopleList = listOf(People("Sam",12),People("Mary",18), People("Sam",13))
// 指定 key : value
val map = peopleList.associate { it.name to it }
// 指定 key , value => 固定為物件
val map2 = peopleList.associateBy { "name:" + it.name }
println(map) // {Sam=People(name=Sam, age=13), Mary=People(name=Mary, age=18)}
println(map2) // {name:Sam=People(name=Sam, age=13), name:Mary=People(name=Mary, age=18)}
}
data class People(
val name:String,
val age: Int
)isEmpty()
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val list1 = listOf(1,2,3,4)
val list2 = emptyList<Int>()
var list3:List<Int>? = null
println(list1.isEmpty()) // flase
println(list2.isEmpty()) // true
println(list3?.isEmpty()) // null
println(list1.orEmpty()) // [1, 2, 3, 4]
println(list2.orEmpty()) // []
println(list3?.orEmpty()) // null
}
take(), takeLast() 取出list 數量
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val numberList = mutableListOf(1,2,3,4,5,6)
// 從前面取兩個
println(numberList.take(2)) // [1, 2]
// 從後面取兩個
println(numberList.takeLast(2)) // [5, 6]
val noneList :List<Int>? = emptyList()
println(noneList?.take(1)) // []
val nullList :List<Int>? = null
println(nullList?.take(1)) // null
}getOrElse() ,getOrNull()
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val list = listOf(1,2,3,4)
println(list.getOrElse(1,{9})) // 1
println(list.getOrElse(5,{9})) // 9
println(list.getOrNull(1)) // 2
println(list.getOrNull(5)) // null
}
Map 相關
containsKey(), 包含 key
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val numberMap = mapOf("one" to 1,"two" to 2)
println(numberMap.containsKey("one")) // true
val worldMap = mapOf("one" to "ONE","two" to "TWO")
println(worldMap.containsValue("one")) // false
println(worldMap.containsValue("ONE")) // true
}
filter{}, filterNot{}, 過濾
filterKeys{}, filterValues{}
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val worldMap = mapOf("one" to "ONE","two" to "TWO", "three" to "THREE")
println(worldMap.filter {it.key.contains("t")}) // {two=TWO, three=THREE}
println(worldMap.filterNot {it.key.contains("t")}) // {one=ONE}
println(worldMap.filterKeys {key -> key.contains("o")}) // {one=ONE, two=TWO}
println(worldMap.filterValues {value -> value.contains("T")}) // {two=TWO, three=THREE}
}
forEach{}
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val map = mapOf("one" to "ONE","two" to "TWO", "three" to "THREE")
for( (key, value) in map ){
println("key:${key}, value:${value}")
}
// key=one, value=ONE
// key=two, value=TWO
// packagekey=three, value=THREE
map.forEach{
println("key:${it.key},value:${it.value}")
}
// key=one, value=ONE
// key=two, value=TWO
// packagekey=three, value=THREE
}
getOrElse()
isEmpty(), isNotEmpty()
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val map = mapOf("one" to "ONE","two" to "TWO", "three" to "THREE")
println(map.getOrElse("one",{"Default"})) // ONE
println(map.getOrElse("four",{"Default"})) // Default
val map2 = mapOf<String,String>()
val map3 :MutableMap<String,String>? = null
println(map.isEmpty()) // false
println(map.isNotEmpty()) // true
println(map.orEmpty()) // {one=ONE, two=TWO, three=THREE}
println(map2.isEmpty()) // true
println(map2.isNotEmpty()) // false
println(map2.orEmpty()) // {}
println(map3?.isEmpty()) // null
println(map3?.isNotEmpty()) // null
println(map3?.orEmpty()) // null
}
count(), 數量, 有條件的數量
import java.util.*
import java.text.SimpleDateFormat
fun main() {
val worldMap = mapOf("one" to "ONE","two" to "TWO", "three" to "THREE")
println(worldMap.count()) // 3
println(worldMap.count{ it.key.contains("t")}) // 2
}