📜  C#|在堆栈顶部获取对象–窥视操作

📅  最后修改于: 2021-05-29 20:44:29             🧑  作者: Mango

堆栈表示对象的后进先出集合。当您需要对项目进行后进先出的访问时使用。在列表中添加项目时,称为推送项目,而在删除项目时,则称为弹出项目。 Stack .Peek方法用于返回Stack 顶部的对象而不将其删除。此方法是O(1)操作。

特性:

  • 堆栈的容量是堆栈可以容纳的元素数量。将元素添加到堆栈后,容量会根据需要通过重新分配自动增加。
  • 如果Count小于堆栈的容量,则Push是O(1)运算。如果需要增加容量以容纳新元素,则Push变为O(n)操作,其中n为Count。 Pop是O(1)运算。
  • 堆栈接受null作为有效值,并允许重复的元素。

句法:

object Peek(); 

返回值: Peek()方法从System.Object类型的Stack 返回最后一个(最上面的)值。

异常:在空堆栈上调用Peek()方法将抛出InvalidOperationException 。因此,在使用Peek()方法检索元素之前,请始终检查堆栈中的元素。

下面给出了一些示例,以更好地理解实现。

范例1:

// C# code to Get object at
// the top of the Stack
using System;
using System.Collections.Generic;
  
class GFG {
  
    // Driver code
    public static void Main()
    {
  
        // Creating a Stack of strings
        Stack myStack = new Stack();
  
        // Inserting the elements into the Stack
        myStack.Push("1st Element");
        myStack.Push("2nd Element");
        myStack.Push("3rd Element");
        myStack.Push("4th Element");
        myStack.Push("5th Element");
        myStack.Push("6th Element");
  
        // Displaying the count of elements
        // contained in the Stack
        Console.Write("Total number of elements in the Stack are : ");
  
        Console.WriteLine(myStack.Count);
  
        // Displaying the top element of Stack
        // without removing it from the Stack
        Console.WriteLine("Element at the top is : " + myStack.Peek());
  
        // Displaying the top element of Stack
        // without removing it from the Stack
        Console.WriteLine("Element at the top is : " + myStack.Peek());
  
        // Displaying the count of elements
        // contained in the Stack
        Console.Write("Total number of elements in the Stack are : ");
  
        Console.WriteLine(myStack.Count);
    }
}

输出:

Total number of elements in the Stack are : 6
Element at the top is : 6th Element
Element at the top is : 6th Element
Total number of elements in the Stack are : 6

范例2:

// C# code to Get object at
// the top of the Stack
using System;
using System.Collections.Generic;
  
class GFG {
  
    // Driver code
    public static void Main()
    {
  
        // Creating a Stack of Integers
        Stack myStack = new Stack();
  
        // Displaying the top element of Stack
        // without removing it from the Stack
        // Calling Peek() method on empty stack
        // will throw InvalidOperationException.
        Console.WriteLine("Element at the top is : " + myStack.Peek());
    }
}

运行时错误:

参考:

  • https://docs.microsoft.com/zh-cn/dotnet/api/system.collections.stack.peek?view=netframework-4.7.2