C＃中的Stack.Peek方法

此方法(位于System.Collections命名空间下)用于在不删除对象的情况下返回堆栈顶部的对象。此方法类似于Pop方法，但是Peek不会修改Stack。

句法：

public virtual object Peek ();

返回值：它返回对象在堆栈的顶部。

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 illustrate the
// Stack.Peek Method
using System;
using System.Collections;
  
class GFG {
  
    // Driver code
    public static void Main()
    {
  
        // Creating a Stack
        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 illustrate the
// Stack.Peek Method
using System;
using System.Collections;
  
class GFG {
  
    // Driver code
    public static void Main()
    {
  
        // Creating a Stack
        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：

Unhandled Exception:
System.InvalidOperationException: Stack empty.

参考：

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