找元素
indexOf : 元素 找 下標
private fun indexOf() {
val mList = listOf(1, 2, 3, 4, 2)
println(mList.indexOf(3))
println(mList.indexOf(0))
println(mList.indexOfFirst { it == 2 })
println(mList.indexOfLast { it == 2 })
}
elementAt : 下標 找 元素
private fun elementAt() {
val mList: MutableList<String> = mutableListOf("a", "b", "c", "d", "e", "f", "g")
println("下標爲5的元素值:${mList.elementAt(5)}")
println(mList.elementAtOrElse(5) { "default value" })
println(mList.elementAtOrElse(10) { "default value" })
println(mList.elementAtOrNull(10))
}
獲取元素
first :
private fun first() {
val mList1 = mutableListOf(0, 1, 2, 3, 4, 5)
println(mList1.first())
val mList2 = listOf<Int>()
println(mList2.firstOrNull())
val mList3 = listOf(1, 2, 3)
println(mList3.first { it % 2 == 0 })
val mList4 = listOf(1, 2, 3)
println(mList4.first { it % 2 == 0 })
}
last :
private fun last() {
val mList1 = mutableListOf(0, 1, 2, 3, 4, 5)
println(mList1.last())
val mList2 = listOf<Int>()
println(mList2.lastOrNull())
val mList3 = listOf(1, 2, 3)
println(mList3.last { it % 2 == 0 })
val mList4 = listOf(1, 2, 3)
println(mList4.lastOrNull { it % 2 == 0 })
}