Java 中的 ConcurrentLinkedDeque peekFirst()方法

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

java . util . concurrentlinkedequest . peek first()是 Java 中的一个内置方法， 在不移除它的情况下检索这个的第一个元素。如果目标为空，该功能返回空。

语法:

Conn_Linked_Deque.peekFirst()

参数:该功能不接受任何参数。

返回值:函数返回这个德格中出现的第一个元素，当德格为空时返回空值。

下面的程序说明了 peekFirst()方法:

程序 1: 该程序涉及到带有整数元素的德克尔。

// Java Program Demonstrate peekFirst()
// method of ConcurrentLinkedDeque

import java.util.concurrent.*;

class ConcurrentLinkedDequeDemo {
    public static void main(String[] args)
    {
        ConcurrentLinkedDeque<Integer> cld =
                    new ConcurrentLinkedDeque<Integer>();

        cld.addFirst(12);
        cld.addFirst(110);
        cld.addFirst(55);
        cld.addFirst(76);

        // Displaying the existing LinkedDeque
        System.out.println("Elements in"
                           + "the LinkedDeque: " + cld);

        // Displaying the first element
        System.out.println("First Element in"
                   + "the LinkedDeque: " + cld.peekFirst());
    }
}

Output:

Elements inthe LinkedDeque: [76, 55, 110, 12]
First Element inthe LinkedDeque: 76

程序二:本程序涉及带有弦元素的德格。

// Java Program Demonstrate peekFirst()
// method of ConcurrentLinkedDeque

import java.util.concurrent.*;

class ConcurrentLinkedDequeDemo {
    public static void main(String[] args)
    {
        ConcurrentLinkedDeque<String> cld = 
                           new ConcurrentLinkedDeque<String>();

        cld.addFirst("GFG");
        cld.addFirst("Gfg");
        cld.addFirst("GeeksforGeeks");
        cld.addFirst("Geeks");

        // Displaying the existing LinkedDeque
        System.out.println("Elements in"
                           + "the LinkedDeque: " + cld);

        // Displaying the First element
        System.out.println("First Element in"
                       + "the LinkedDeque: " + cld.peekFirst());
    }
}

Output:

Elements inthe LinkedDeque: [Geeks, GeeksforGeeks, Gfg, GFG]
First Element inthe LinkedDeque: Geeks

参考:https://docs . Oracle . com/javase/8/docs/API/Java/util/concurrentlinkedeque . html # peek first()

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