Java中的 LinkedBlockingDeque pop() 方法

LinkedBlockingDeque的pop()方法从这个双端队列表示的堆栈中弹出一个元素。换句话说，它删除并返回此双端队列的第一个元素。如果容器为空，则返回null 。

句法：

public E pop()

参数：此方法不接受任何参数。

返回：此方法返回此双端队列前面的元素（这是此双端队列表示的堆栈的顶部）。如果双端队列为空，它会抛出NoSuchElementException 。

下面的程序说明了 LinkedBlockingDeque 的 pop() 方法：

方案一：

// Java Program to demonstrate pop()
// method of LinkedBlockingDeque
  
import java.util.concurrent.LinkedBlockingDeque;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
        throws NoSuchElementException
    {
  
        // create object of LinkedBlockingDeque
        LinkedBlockingDeque LBD
            = new LinkedBlockingDeque();
  
        // Add numbers to end of LinkedBlockingDeque
        LBD.addFirst(7855642);
        LBD.addFirst(35658786);
        LBD.addFirst(5278367);
        LBD.addFirst(74381793);
  
        // Print the queue
        System.out.println("Linked Blocking Deque: " + LBD);
  
        // prints and deletes
        System.out.println("Front element in Deque: " + LBD.pop());
  
        // Deque after deletion of front element
        System.out.println("Linked Blocking Deque: " + LBD);
    }
}

输出：

Linked Blocking Deque: [74381793, 5278367, 35658786, 7855642]
Front element in Deque: 74381793
Linked Blocking Deque: [5278367, 35658786, 7855642]

方案二：

// Java Program Demonstrate pop()
// method of LinkedBlockingDeque
// when Deque is empty
  
import java.util.concurrent.LinkedBlockingDeque;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
  
    {
  
        // create object of LinkedBlockingDeque
        LinkedBlockingDeque LBD
            = new LinkedBlockingDeque();
  
        // Add numbers to end of LinkedBlockingDeque
        LBD.add(7855642);
        LBD.add(35658786);
        LBD.add(5278367);
        LBD.add(74381793);
  
        // empty deque
        LBD.clear();
  
        System.out.println("Front element in Deque: " + LBD.pop());
    }
}

输出：

Exception in thread "main" java.util.NoSuchElementException
    at java.util.concurrent.LinkedBlockingDeque.removeFirst(LinkedBlockingDeque.java:453)
    at java.util.concurrent.LinkedBlockingDeque.pop(LinkedBlockingDeque.java:777)
    at GFG.main(GFG.java:27)

参考： https: Java/util/concurrent/LinkedBlockingDeque.html#pop()