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