Java ArrayDeque peekFirst()用法及代碼示例

Java中的java.util.ArrayDeque.peekFirst()方法用於檢索或獲取雙端隊列的第一個元素。檢索到的元素不會從Queue中刪除或刪除，該方法僅返回它。如果雙端隊列中沒有元素或該元素為空，則返回Null。

用法:

Array_Deque.peekFirst()

參數：該方法不帶任何參數。

返回值：該方法返回雙端隊列的第一個元素。

下麵的程序演示了Java.util.ArrayDeque.peekFirst()方法：
示例1:

// Java code to illustrate peekFirst() 
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("Initial ArrayDeque: " + de_que); 
  
        // Displaying the first element 
        System.out.println("The first element is: " +  
                                           de_que.peekFirst()); 
  
        // Displaying the ArrayDeque after operation 
        System.out.println("Final ArrayDeque: " + de_que); 
    } 
}

輸出：

Initial ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
The first element is: Welcome
Final ArrayDeque: [Welcome, To, Geeks, 4, Geeks]

示例2:

// Java code to illustrate peekFirst() 
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("Initial ArrayDeque: " + de_que); 
  
        // Displaying the first element 
        System.out.println("The first element is: " +  
                                           de_que.peekFirst()); 
  
        // Displaying the ArrayDeque after operation 
        System.out.println("Final ArrayDeque: " + de_que); 
    } 
}

輸出：

Initial ArrayDeque: [10, 15, 30, 20, 5]
The first element is: 10
Final ArrayDeque: [10, 15, 30, 20, 5]

示例3:對於空的雙端隊列：

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

輸出：

ArrayDeque: []
The first element 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 peekFirst() 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。