java Java 中的 ConcurrentLinkedDeque offerFirst()方法

Java 中的 ConcurrentLinkedDeque offerFirst()方法

原文:https://www . geeksforgeeks . org/concurrentlinkedeque-offer first-method-in-Java/

java . util . concurrentlinkeDeque . offer first()方法是 Java 中的一个内置方法，它将作为参数传递的指定元素插入到 deque 的前面。

语法:

Conn_Linked_Deque.offerFirst*(Object elem)*

参数:该方法接受一个参数 elem ，该参数指定了要插入到背景前面的元素。

返回值:如果元素成功添加到德格中，函数返回真，否则返回假。

异常:如果传递的参数为空，则函数抛出空指针异常。

下面的程序说明了 concurrentlinkedrequest . offer first()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

程序二:

/* 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