Java ConcurrentLinkedDeque peek()方法及示例

Java中的java.util.ConcurrentLinkedDeque.peek()方法是用来检索或获取Deque头部的元素的。检索到的元素不会被删除或从Deque中移除，相反，该方法只是返回它。如果Deque中没有任何元素，则会返回Null。

语法

Array_Deque.peek()

参数： 该方法不接受任何参数。

返回值： 该方法返回Deque头部的元素。

下面的程序说明了Java.util.ConcurrentLinkedDeque.peek()方法。

程序1 :

// Java code to illustrate peek()
  
import java.util.concurrent.*;
  
public class ConcurrentLinkedDequeDemo {
    public static void main(String args[])
    {
        // Creating an empty ConcurrentLinkedDeque
        ConcurrentLinkedDeque<String> de_que
            = new ConcurrentLinkedDeque<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 ConcurrentLinkedDeque
        System.out.println("Initial ConcurrentLinkedDeque: "
                           + de_que);
  
        // Displaying the head
        System.out.println("The element at head is: "
                           + de_que.peek());
  
        // Displaying the ConcurrentLinkedDeque after operation
        System.out.println("Final ConcurrentLinkedDeque: "
                           + de_que);
    }
}

输出。

Initial ConcurrentLinkedDeque: [Welcome, To, Geeks, 4, Geeks]
The element at head is: Welcome
Final ConcurrentLinkedDeque: [Welcome, To, Geeks, 4, Geeks]

代码2 。

// Java code to illustrate peek()
import java.util.concurrent.*;
  
public class ConcurrentLinkedDequeDemo {
    public static void main(String args[])
    {
        // Creating an empty ConcurrentLinkedDeque
        ConcurrentLinkedDeque<Integer> de_que
            = new ConcurrentLinkedDeque<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 ConcurrentLinkedDeque
        System.out.println("Initial ConcurrentLinkedDeque: "
                           + de_que);
  
        // Displaying the head
        System.out.println("The element at head is: "
                           + de_que.peek());
  
        // Displaying the ConcurrentLinkedDeque after operation
        System.out.println("Final ConcurrentLinkedDeque: "
                           + de_que);
    }
}

输出。

Initial ConcurrentLinkedDeque: [10, 15, 30, 20, 5]
The element at head is: 10
Final ConcurrentLinkedDeque: [10, 15, 30, 20, 5]

程序3： 对于一个空deque。

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

输出。

ConcurrentLinkedDeque: []
The element at head is: null