java - 在 kotlin 中使用大小初始化 ArrayList<ArrayList<Int>>

Question

我正在尝试在构造函数中初始化一个具有大小的列表。但是我的列表的大小是 0。

val seqList = ArrayList<ArrayList<Int>>(N) // This has the Problem
val queries = ArrayList<Query>(Q) // This works like a charm

两个都有N和 Q设置为来自用户的非零输入让我们说 N = 100和 Q = 100

在调试我的代码时，我发现 queries.size() = 100但是 seqList.size() = 0

我的假设是不正确的，seqList也应该用 N ArrayList<Int> 初始化对象。

Answer 1

恐怕你的假设不正确。

引自 documentation ArrayList:

Provides a MutableList implementation, which uses a resizable array as its backing storage.

This implementation doesn't provide a way to manage capacity, as backing JS array is resizeable itself. There is no speed advantage to pre-allocating array sizes in JavaScript, so this implementation does not include any of the capacity and "growth increment" concepts.

特别是构造函数:

ArrayList(initialCapacity = 0))

Creates an empty ArrayList.

创建了一个empty ArrayList，因此提供100作为参数不会在列表中创建元素。