Java中的Stack peek（）方法-yiteyi-C++库

爪哇。util。堆栈Java中的peek（）方法用于检索或获取堆栈的第一个元素或堆栈顶部的元素。检索到的元素不会被删除或从堆栈中移除。

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语法：

STACK.peek()

参数： 该方法不采用任何参数。

返回值： 该方法返回堆栈顶部的元素，如果堆栈为空，则返回NULL。

例外情况： 方法抛出 EmptyStackException 如果堆栈是空的。

下面的程序演示了java。util。堆栈peek（）方法： 项目1：

                     // Java code to illustrate peek() function                   
                             
                     import                               java.util.*;                   
                             
                     public                               class                               StackDemo {                   
                                         public                               static                               void                               main(String args[])                   
                                         {                   
                                         // Creating an empty Stack                   
                                         Stack<String> STACK =                               new                               Stack<String>();                   
                             
                                         // Use push() to add elements into the Stack                   
                                         STACK.push(                               "Welcome"                               );                   
                                         STACK.push(                               "To"                               );                   
                                         STACK.push(                               "Geeks"                               );                   
                                         STACK.push(                               "For"                               );                   
                                         STACK.push(                               "Geeks"                               );                   
                             
                                         // Displaying the Stack                   
                                         System.out.println(                               "Initial Stack: "                               + STACK);                   
                             
                                         // Fetching the element at the head of the Stack                   
                                         System.out.println(                               "The element at the top of the"                   
                                         +                               " stack is: "                               + STACK.peek());                   
                             
                                         // Displaying the Stack after the Operation                   
                                         System.out.println(                               "Final Stack: "                               + STACK);                   
                                         }                   
                     }                   

输出：

Initial Stack: [Welcome, To, Geeks, For, Geeks]
The element at the top of the stack is: Geeks
Final Stack: [Welcome, To, Geeks, For, Geeks]

项目2：

                     // Java code to illustrate peek() function                   
                             
                     import                               java.util.*;                   
                             
                     public                               class                               StackDemo {                   
                                         public                               static                               void                               main(String args[])                   
                                         {                   
                                         // Creating an empty Stack                   
                                         Stack<Integer> STACK =                               new                               Stack<Integer>();                   
                             
                                         // Use push() to add elements into the Stack                   
                                         STACK.push(                               10                               );                   
                                         STACK.push(                               15                               );                   
                                         STACK.push(                               30                               );                   
                                         STACK.push(                               20                               );                   
                                         STACK.push(                               5                               );                   
                             
                                         // Displaying the Stack                   
                                         System.out.println(                               "Initial Stack: "                               + STACK);                   
                             
                                         // Fetching the element at the head of the Stack                   
                                         System.out.println(                               "The element at the top of the"                   
                                         +                               " stack is: "                               + STACK.peek());                   
                             
                                         // Displaying the Stack after the Operation                   
                                         System.out.println(                               "Final Stack: "                               + STACK);                   
                                         }                   
                     }                   

输出：

Initial Stack: [10, 15, 30, 20, 5]
The element at the top of the stack is: 5
Final Stack: [10, 15, 30, 20, 5]

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