Java BlockingDeque pollFirst()用法及代碼示例

BlockingDeque的pollFirst()方法返回Deque容器中的front元素，並將其刪除。如果容器為空，則返回null。

用法:

public E pollFirst()

參數：此方法不接受任何參數。

返回值：如果容器不為空，則此方法在Deque容器中返回front元素，並刪除該元素。如果容器為空，則返回null。

注意：BlockingDeque的pollFirst()方法已從Java中的LinkedBlockingDeque類繼承。

以下示例程序旨在說明BlockingDeque的pollFirst()方法：

示例1:

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

輸出：

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

示例2:

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

輸出：

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

參考： https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingDeque.html#pollFirst(long, %20java.util.concurrent.TimeUnit)

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注：本文由純淨天空篩選整理自gopaldave大神的英文原創作品 BlockingDeque pollFirst() method in Java with examples。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。