peek()java_Java Stack peek()用法及代码示例

Java中的java.util.Stack.peek()方法用于检索或获取Stack的第一个元素或位于Stack顶部的元素。检索到的元素不会被删除或从堆栈中删除。

用法:

STACK.peek()

参数：该方法不带任何参数。

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：如果堆栈为空，则该方法引发EmptyStackException。

以下程序说明了java.util.Stack.peek()方法：

示例1:

// Java code to illustrate peek() function

import java.util.*;

public class StackDemo {

public static void main(String args[])

{

// Creating an empty Stack

Stack STACK = new Stack();

// 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 STACK = new Stack();

// 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]