C＃|创建具有指定初始容量的ArrayList

ArrayList(Int32)构造函数用于初始化ArrayList类的新实例，该实例将为空并具有指定的初始容量。 ArrayList表示可以单独索引的对象的有序集合。基本上，它是数组的替代方法。它还允许动态分配内存，添加，搜索和排序列表中的项目。

Syntax: public ArrayList (int capacity);

Here, capacity is the number of elements that the new list can initially store.

Exception: This will give ArgumentOutOfRangeException if the capacity is less than zero.

重要事项：

• ArrayList可以容纳的元素数称为ArrayList的容量。如果将元素添加到ArrayList中，则将通过重新分配内部数组来自动增加容量。
• 如果可以估计集合的大小，则指定初始容量将消除在将元素添加到ArrayList时执行大量调整大小操作的需求。
• 此构造函数是O(n)运算，其中n是容量。

下面的程序说明了上面讨论的构造函数的用法：

范例1：

// C# Program to illustrate how
// to create a ArrayList having
// specified initial capacity
using System;
using System.Collections;
  
class Geeks {
  
    // Main Method
    public static void Main(String[] args)
    {
  
        // arrlist is the ArrayList object
        // ArrayList(10) is the constructor
        // used to initializes a new
        // instance of the ArrayList class
        // having 10 as capacity
        ArrayList arrlist = new ArrayList(10);
  
        Console.Write("Number of elements: ");
          
        // Count property is used to get the
        // number of elements in ArrayList
        // It will give 0 as no elements 
        // are present
        Console.WriteLine(arrlist.Count);
  
        Console.Write("Capacity of ArrayList: ");
          
        // using capacity property
        Console.WriteLine(arrlist.Capacity);
          
        // inserting elements to ArrayList
        arrlist.Add("C");
        arrlist.Add("C++");
        arrlist.Add("Java");
        arrlist.Add("C#");
          
        Console.Write("Number of elements: ");
          
        // Count property is used to get the
        // number of elements in ArrayList
        Console.WriteLine(arrlist.Count);
  
        Console.Write("Capacity of ArrayList: ");
          
        // using capacity property
        Console.WriteLine(arrlist.Capacity);
    }
}

输出：

Number of elements: 0
Capacity of ArrayList: 10
Number of elements: 4
Capacity of ArrayList: 10

示例2：对于ArgumentOutOfRangeException

// C# Program to illustrate how
// to create a ArrayList having
// specified initial capacity
using System;
using System.Collections;
  
class Geeks {
  
    // Main Method
    public static void Main(String[] args)
    {
  
        // arrlist is the ArrayList object
        // taking capacity less than zero
        ArrayList arrlist = new ArrayList(-4);
  
        // using capacity property
        Console.WriteLine(arrlist.Capacity);
    }
}

运行时错误：

Unhandled Exception:
System.ArgumentOutOfRangeException: ‘capacity’ must be non-negative.
Parameter name: capacity

参考：

• https://docs.microsoft.com/zh-cn/dotnet/api/system.collections.arraylist.-ctor?view=netframework-4.7.2#System_Collections_ArrayList__ctor_System_Int32_