Java ConcurrentLinkedDeque offerFirst()用法及代码示例

java.util.concurrent.ConcurrentLinkedDeque.offerFirst()方法是Java中的一种内置方法，它将作为参数传递的指定元素插入双端队列的前面。

用法:

Conn_Linked_Deque.offerFirst(Object elem)

参数：该方法接受参数elem，以选择要插入双端队列的元素的元素。

返回值：如果将元素成功添加到双端队列中，则该函数返回True，否则返回False。

异常：如果传递的参数为NULL，则该函数将引发NullPointerException。

以下示例程序旨在说明ConcurrentLinkedDeque.offerFirst()方法：

程序1：

/* Java Program to Demonstrate offerFirst() 
   method of ConcurrentLinkedDeque */
  
import java.util.concurrent.*; 
class GFG { 
    public static void main(String[] args) 
    { 
  
        // Creating an empty Deque 
        ConcurrentLinkedDeque<String> cld =  
                     new ConcurrentLinkedDeque<String>(); 
  
        // Add elements into the Deque 
        cld.add("Welcome"); 
        cld.add("To"); 
        cld.add("Geeks"); 
        cld.add("4"); 
        cld.add("Geeks"); 
  
        // Displaying the Deque 
        System.out.println("Elements in Deque: "
                           + cld); 
  
        // Displaying the First element 
        System.out.println("The First element is: " +  
                                       cld.getFirst()); 
  
        /* Insert an element at the front 
            of the deque */
        if (cld.offerFirst("GFG")) { 
            // Displaying the First element 
            System.out.println("The Inserted element is: " +  
                                             cld.getFirst()); 
        } 
  
        // Displaying the Deque 
        System.out.println("Elements in Deque: "
                           + cld); 
  
        // Displaying the First element 
        System.out.println("The First element is: " +  
                                      cld.getFirst()); 
    } 
}

输出：

Elements in Deque: [Welcome, To, Geeks, 4, Geeks]
The First element is: Welcome
The Inserted element is: GFG
Elements in Deque: [GFG, Welcome, To, Geeks, 4, Geeks]
The First element is: GFG

示例2:

/* Java Program to Demonstrate offerFirst() 
   method of ConcurrentLinkedDeque */
  
import java.util.concurrent.*; 
class GFG { 
    public static void main(String[] args) 
    { 
  
        // Creating an empty Deque 
        ConcurrentLinkedDeque<Integer> cld = 
                   new ConcurrentLinkedDeque<Integer>(); 
  
        // Add elements into the Deque 
        cld.add(12); 
        cld.add(43); 
        cld.add(29); 
        cld.add(16); 
        cld.add(70); 
  
        // Displaying the Deque 
        System.out.println("Elements in Deque: "
                           + cld); 
  
        // Displaying the First element 
        System.out.println("The First element is: " +  
                                     cld.getFirst()); 
  
        try { 
            cld.offerFirst(null); 
        } 
        catch (Exception e) { 
            System.out.println(e); 
        } 
  
        /* Insert an element at the front 
            of the deque */
        if (cld.offerFirst(74)) { 
            // Displaying the First element 
            System.out.println("The Inserted element is: " +  
                                            cld.getFirst()); 
        } 
  
        // Displaying the Deque 
        System.out.println("Elements in Deque: "
                           + cld); 
  
        // Displaying the First element 
        System.out.println("The First element is: " +  
                                      cld.getFirst()); 
    } 
}

输出：

Elements in Deque: [12, 43, 29, 16, 70]
The First element is: 12
java.lang.NullPointerException
The Inserted element is: 74
Elements in Deque: [74, 12, 43, 29, 16, 70]
The First element is: 74

参考： https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentLinkedDeque.html#offerFirst()

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注：本文由纯净天空筛选整理自RICHIK BHATTACHARJEE大神的英文原创作品 ConcurrentLinkedDeque offerFirst() 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。