可变与不可变集合

集合 - 图1

  • kotlin 集合底层也是调用 Java API
  • 不可变，不能添加和删除元素

集合创建

  1.         val listOf:List<Int> = listOf(1, 2, 3)
  2.         var mutableList:MutableList<Any> = mutableListOf(1, 2, 3)
  1.         val map1 = mapOf("key" to "value", "name" to "july")
  2.         var map2 = mutableMapOf("key" to "value", "name" to "july")

集合新增修改

  1.     private fun testUpdateCollection() {
  2.         var mutableList: MutableList<Any> = mutableListOf(1, 12, 3)
  3.         mutableList.add(10)
  4.         mutableList.remove(555)
  5.         println(mutableList.joinToString())
  6.     }

集合读取

  1.         var mutableList: MutableList<Any> = mutableListOf(1, 12, 3)
  2.         println(mutableList[2])
  3.         mutableList[2]=20;

集合遍历

  1.     private fun testIterateCollection() {
  2.         val listOf: List<Int> = listOf(11, 22, 33)
  3.         for (i in listOf) {
  4.             println("for $i")
  5.         }
  6.         listOf.forEach {
  7.             println("forEach = $it")
  8.         }
  9.     }

遍历带下标

  2.         val listOf: List<Int> = listOf(11, 22, 33)
  3.         for ((index, value) in listOf.withIndex()) {
  4.             println("The element at $index is $value")
  5.         }

输出：

  1.  The element at 0 is 11
  2.  The element at 1 is 22
  3.  The element at 2 is 33

Pair

  1.     private fun testPair() {
  2.         var pair1 = Pair("a", "b")
  3.         val pair2: Pair<String, Int> = "a" to 3
  4.         println(pair1.first) //访问第1个参数
  5.         println(pair1.second)//访问第2个参数
  6.         val (key,value)=pair2 //解构
  7.     }

Triple

    private fun testTriple() {
        var triple = Triple("a", "b",true)
        println(triple.first)
        println(triple.second)
        println(triple.third)
        val (one,two,three)=triple //解构
    }