Java 中的 Stack.peek() 方法

Java 中的 java.util.Stack.peek() 方法用于检索或获取 Stack 中的第一个元素或顶部的元素。所检索的元素不会从 Stack 中删除或移除。

语法：

STACK.peek()

参数： 该方法不接受任何参数。

返回值： 该方法返回 Stack 顶部的元素，如果 Stack 为空，则返回 NULL。

异常： 如果堆栈为空，则该方法抛出 EmptyStackException。

以下程序说明了 java.util.Stack.peek() 方法：
程序 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);
    }
}

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

程序 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);
    }
}

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