Java BlockingQueue poll()用法及代码示例

BlockingQueue接口的poll(long timeout，TimeUnit unit)方法通过从队列中删除该元素来返回BlockingQueue的头部。可以说此方法从此LinkedBlockingQueue的头部检索并删除了元素。如果队列为空，则poll()方法将等待直到指定时间元素可用。

用法:

public E poll(long timeout, TimeUnit unit) throws

参数：此方法采用两个强制性参数：

timeout–等待的时间，以单位为单位。
unit–超时参数的TimeUnit。

返回值：此方法从此LinkedBlockingQueue的头部检索并删除元素，如果在元素可用之前经过了指定的等待时间，则为null。

异常如果在等待元素可用时方法被中断，则此方法将引发InterruptedException。

注意：BlockingQueue的poll()方法已从Java中的Queue类继承。

以下示例程序旨在说明BlockingQueue的poll(长时间超时，TimeUnit单位)方法：

程序1：

// Java program to demonstrate 
// poll(long timeout, TimeUnit unit) 
// method of LinkedBlockingQueue 
  
import java.util.concurrent.LinkedBlockingQueue; 
import java.util.concurrent.BlockingQueue; 
import java.util.concurrent.TimeUnit; 
  
public class GFG { 
  
    public static void main(String[] args) 
        throws InterruptedException 
    { 
        // define capacity of BlockingQueue 
        int capacityOfQueue = 4; 
  
        // create object of BlockingQueue 
        BlockingQueue<String> BQ 
            = new LinkedBlockingQueue<String>(capacityOfQueue); 
  
        // Add element to BlockingQueue 
        BQ.add("Ravi"); 
        BQ.add("Suraj"); 
        BQ.add("Harsh"); 
  
        // print elements of queue 
        System.out.println("Items in Queue are " + BQ); 
  
        // Try to poll elements from BQ 
        // using poll(long timeout, TimeUnit unit) method 
        System.out.println("Removing item From head: "
                           + BQ.poll(5, TimeUnit.SECONDS)); 
  
        // print queue details 
        System.out.println("Now Queue Contains" + BQ); 
  
        // using poll(long timeout, TimeUnit unit) method 
        System.out.println("Removing item From head: "
                           + BQ.poll(5, TimeUnit.SECONDS)); 
  
        // print queue details 
        System.out.println("Now Queue Contains" + BQ); 
  
        // using poll(long timeout, TimeUnit unit) method 
        System.out.println("Removing item From head: "
                           + BQ.poll(5, TimeUnit.SECONDS)); 
  
        // print queue details 
        System.out.println("Now Queue Contains" + BQ); 
  
        // using poll(long timeout, TimeUnit unit) method 
        System.out.println("Removing item From head: "
                           + BQ.poll(5, TimeUnit.SECONDS)); 
        // print queue details 
        System.out.println("Now Queue Contains" + BQ); 
    } 
}

输出：

Items in Queue are [Ravi, Suraj, Harsh]
Removing item From head: Ravi
Now Queue Contains[Suraj, Harsh]
Removing item From head: Suraj
Now Queue Contains[Harsh]
Removing item From head: Harsh
Now Queue Contains[]
Removing item From head: null
Now Queue Contains[]

程序2：

// Java program to demonstrate 
// poll(long timeout, TimeUnit unit) 
// method of LinkedBlockingQueue 
  
import java.util.concurrent.LinkedBlockingQueue; 
import java.util.concurrent.BlockingQueue; 
import java.util.concurrent.TimeUnit; 
  
public class GFG { 
  
    public static void main(String[] args) 
        throws InterruptedException 
    { 
        // define capacity of BlockingQueue 
        int capacityOfQueue = 2; 
  
        // create object of BlockingQueue 
        BlockingQueue<String> BQ 
            = new LinkedBlockingQueue<String>(capacityOfQueue); 
  
        // Add element to BlockingQueue 
        BQ.add("Gopal"); 
        BQ.add("GFG"); 
  
        // print elements of queue 
        System.out.println("Items in Queue are " + BQ); 
  
        // Try to poll elements from BQ 
        // using poll(long timeout, TimeUnit unit) method 
        System.out.println("Removing item From head: "
                           + BQ.poll(2, TimeUnit.SECONDS)); 
  
        // print queue details 
        System.out.println("Now Queue Contains" + BQ); 
    } 
}

输出：

Items in Queue are [Gopal, GFG]
Removing item From head: Gopal
Now Queue Contains[GFG]

参考： https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html#poll(long, %20java.util.concurrent.TimeUnit)

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注：本文由纯净天空筛选整理自gopaldave大神的英文原创作品 BlockingQueue poll() method in Java with examples。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。