Kotlin 集合之 迭代器 Iterator

使用迭代器的方式

只要实现了Iterable接口的类型，都提供迭代器。

下面是使用迭代器的3种方式：

1. 使用next()

   val numbers = listOf("one", "two", "three", "four")
   val numbersIterator = numbers.iterator()
   while (numbersIterator.hasNext()) {
       println(numbersIterator.next())
   }

2. 使用for...in

   val numbers = listOf("one", "two", "three", "four")
   for (item in numbers) {
       println(item)
   }

3. 使用forEach()

   val numbers = listOf("one", "two", "three", "four")
   numbers.forEach {
       println(it)
   }

List 的迭代器

List 的迭代器是ListIterator类型，可以反向迭代：

val numbers = listOf("one", "two", "three", "four")
val listIterator = numbers.listIterator()
while (listIterator.hasNext()) listIterator.next()
println("Iterating backwards:")
while (listIterator.hasPrevious()) {
    print("Index: ${listIterator.previousIndex()}")
    println(", value: ${listIterator.previous()}")
}

// Iterating backwards:
// Index: 3, value: four
// Index: 2, value: three
// Index: 1, value: two
// Index: 0, value: one

可变迭代器

可变集合（MutableList, MutableSet, MutableMap）的迭代器都是MutableIterator类型，可以在迭代的过程中调用remove()方法删除元素。

val numbers = mutableListOf("one", "two", "three", "four") 
val mutableIterator = numbers.iterator()

mutableIterator.next()
mutableIterator.remove()

println("After removal: $numbers")
// After removal: [two, three, four]

另外，MutableList的迭代器是MutableListIterator类型，可以在迭代过程中插入或替换元素。

val numbers = mutableListOf("one", "four", "four") 
val mutableListIterator = numbers.listIterator()

mutableListIterator.next()
mutableListIterator.add("two")
mutableListIterator.next()
mutableListIterator.set("three")

println(numbers)
// [one, two, three, four]