【Treeman】Kotlin 相關

【Kotilin】延伸閱讀

未完成程式碼



【反射】取得目前方法的名稱

/*

* 取得呼叫此方法的 methodName

*/

fun getMethodName(clazz: Any) {

 var fullName = ""

 

 val stackTrace = Thread.currentThread().stackTrace

 if (stackTrace.size >= 3) {

 val methodName = stackTrace[2].methodName

 if (methodName.isEmpty() || className.isEmpty()) {

 return redisEnable

 }

 fullName = "${className}.${methodName}"

 }

 }

tip



null 判斷 ?:

`(判斷式) ?: 0` 是 Kotlin 中的 Elvis 運算符。Elvis 運算符用於簡化空值檢查，它的語法形式是 `?:`。

具體地說，`(判斷式) ?: 0` 表示如果判定式的值不為 null，則使用判定式的值；如果判定式的值為 null，則使用後面的默認值 0。

下面是一個例子：

val result: Int? = someNullableValue // 假設 someNullableValue 是一個可能為 null 的變量

val finalResult = result ?: 0

println("最終結果是 $finalResult")

在這個例子中，如果 `someNullableValue` 不為 null，則 `finalResult` 將被賦值為 `someNullableValue` 的值；如果 `someNullableValue` 為 null，則 `finalResult` 將被賦值為默認值 0。

這種寫法可以簡化空值檢查，使代碼更加簡潔。Elvis 運算符的一般形式是 `expression ?: defaultValue`，其中 `expression` 是要檢查的表達式，而 `defaultValue` 是在表達式為 null 時使用的默認值。【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

 

}

 【Kotilin】基本型別

【Kotlin】coroutines

【MockK】Kotlin Mocking Library