Java ArrayDeque pollFirst()用法及代碼示例

Java中的java.util.ArrayDeque.pollFirst()方法用於檢索或獲取並刪除Deque的第一個元素。 peekFirst()方法僅檢索了第一個元素，但pollFirst()也隨檢索一起刪除了該元素。如果雙端隊列為空，則返回NULL。

用法:

Array_Deque.pollFirst()

參數：該方法不帶任何參數。

返回值：該方法刪除Deque的第一個元素並返回該元素。如果雙端隊列為空，則返回NULL。

下麵的程序演示了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); 
    } 
}

輸出：

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); 
    } 
}

輸出：

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

示例3:對於空的雙端隊列：

// 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()); 
    } 
}

輸出：

ArrayDeque: []
The element at head is: null

相關用法

注：本文由純淨天空篩選整理自Chinmoy Lenka大神的英文原創作品 ArrayDeque pollFirst() Method in Java。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。