Java ArrayDeque pollFirst()用法及代码示例

Java中的java.util.ArrayDeque.pollFirst()方法用于检索或获取并删除Deque的第一个元素。 peekFirst()方法仅检索了第一个元素，但pollFirst()也随检索一起删除了该元素。如果双端队列为空，则返回NULL。

用法:

Array_Deque.pollFirst()

参数：该方法不带任何参数。

返回值：该方法删除Deque的第一个元素并返回该元素。如果双端队列为空，则返回NULL。

下面的程序演示了Java.util.ArrayDeque.pollFirst()方法：
示例1:

// Java code to illustrate pollFirst() 
import java.util.*; 
  
public class ArrayDequeDemo { 
    public static void main(String args[]) 
    { 
        // Creating an empty ArrayDeque 
        Deque<String> de_que = new ArrayDeque<String>(); 
  
        // Use add() method to add elements into the Deque 
        de_que.add("Welcome"); 
        de_que.add("To"); 
        de_que.add("Geeks"); 
        de_que.add("4"); 
        de_que.add("Geeks"); 
  
        // Displaying the ArrayDeque 
        System.out.println("ArrayDeque: " + de_que); 
  
        // Displaying the first element 
        System.out.println("The element at head is: " +  
                                     de_que.pollFirst()); 
  
        // Displaying the final ArrayDeque 
        System.out.println("ArrayDeque after operation: " 
                                                + de_que); 
    } 
}

输出：

ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
The element at head is: Welcome
ArrayDeque after operation: [To, Geeks, 4, Geeks]

示例2:

// Java code to illustrate pollFirst() 
import java.util.*; 
  
public class ArrayDequeDemo { 
    public static void main(String args[]) 
    { 
        // Creating an empty ArrayDeque 
        Deque<Integer> de_que = new ArrayDeque<Integer>(); 
  
        // Use add() method to add elements into the Deque 
        de_que.add(10); 
        de_que.add(15); 
        de_que.add(30); 
        de_que.add(20); 
        de_que.add(5); 
  
        // Displaying the ArrayDeque 
        System.out.println("ArrayDeque: " + de_que); 
  
        // Displaying the first element 
        System.out.println("The element at head is: " +  
                                    de_que.pollFirst()); 
  
        // Displaying the final ArrayDeque 
        System.out.println("ArrayDeque after operation: " 
                                                + de_que); 
    } 
}

输出：

ArrayDeque: [10, 15, 30, 20, 5]
The element at head is: 10
ArrayDeque after operation: [15, 30, 20, 5]

示例3:对于空的双端队列：

// Java code to illustrate pollFirst() 
import java.util.*; 
  
public class ArrayDequeDemo { 
    public static void main(String args[]) 
    { 
        // Creating an empty ArrayDeque 
        Deque<Integer> de_que = new ArrayDeque<Integer>(); 
  
        // Displaying the ArrayDeque 
        System.out.println("ArrayDeque: " + de_que); 
  
        // Displaying the first 
        System.out.println("The element at head is: " +  
                                      de_que.pollFirst()); 
    } 
}

输出：

ArrayDeque: []
The element at head is: null

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注：本文由纯净天空筛选整理自Chinmoy Lenka大神的英文原创作品 ArrayDeque pollFirst() Method in Java。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。