Java Stack peek()方法

Java中的java.util.Stack.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。取回的元素不会被删除或从堆栈中删除。

语法

STACK.peek()

参数： 该方法不接受任何参数。

返回值： 该方法返回堆栈顶部的元素，如果堆栈为空，则返回NULL。

异常： 如果堆栈是空的，该方法会抛出EmptyStackException。

下面的程序说明了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);
    }
}

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]

示例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]