Java LinkedBlockingDeque pop()方法

LinkedBlockingDeque 的 pop() 方法从这个deque所代表的堆栈中弹出一个元素。换句话说，它删除并返回这个deque的第一个元素。如果容器是空的，它将返回 null 。

语法

public E pop()

参数： 该方法不接受任何参数。

返回： 该方法返回该deque前面的元素（也就是该deque所代表的堆栈的顶部）。如果deque是空的，它会抛出一个 NoSuchElementException 。

下面的程序说明了LinkedBlockingDeque的pop()方法。

程序1 :

// 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<Integer> LBD
            = new LinkedBlockingDeque<Integer>();
  
        // 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]

示例2

// 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<Integer> LBD
            = new LinkedBlockingDeque<Integer>();
  
        // 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)

参考资料: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/LinkedBlockingDeque.html#pop()