LinkedBlockingQueue中有两种poll()方法。
poll()
LinkedBlockingQueue的poll()方法通过从队列中删除该元素来返回LinkedBlockingQueue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,则轮询方法返回null。
用法:
public E poll()
返回值:此方法从此LinkedBlockingQueue的头部检索并删除元素。如果队列为空,则返回null。
以下示例程序旨在说明LinkedBlockingQueue类的poll()方法:
示例1:使用poll()方法从LinkedBlockingQueue中删除元素,其中LinkedBlockingQueue包含名称列表。
// Java Program Demonstrate poll()
// method of LinkedBlockingQueue
import java.util.concurrent.LinkedBlockingQueue;
public class GFG {
public static void main(String[] args)
{
// define capacity of LinkedBlockingQueue
int capacityOfQueue = 4;
// create object of LinkedBlockingQueue
LinkedBlockingQueue<String> linkedQueue
= new LinkedBlockingQueue<String>(capacityOfQueue);
// Add element to LinkedBlockingQueue
linkedQueue.add("Ravi");
linkedQueue.add("Suraj");
linkedQueue.add("Harsh");
linkedQueue.add("Sayan");
// print elements of queue
System.out.println("Items in Queue are " + linkedQueue);
// we want to remove two elements from queue from head
// Applying poll() method on queue to remove element
String removedItem1 = linkedQueue.poll();
// print removedItem and queue
System.out.println("Removed Item is " + removedItem1);
// print elements of queue after removing first item
System.out.println("Remaining Items in Queue are "
+ linkedQueue);
// Applying poll() method on queue to remove another element
String removedItem2 = linkedQueue.poll();
// print removedItem and queue
System.out.println("Removed Item is " + removedItem2);
// print elements of queue after removing first item
System.out.println("Remaining Items in Queue are " + linkedQueue);
}
}
Items in Queue are [Ravi, Suraj, Harsh, Sayan] Removed Item is Ravi Remaining Items in Queue are [Suraj, Harsh, Sayan] Removed Item is Suraj Remaining Items in Queue are [Harsh, Sayan]
示例2:从包含雇员列表的LinkedBlockingQueue中删除元素,如果队列为空,则打印null。
// Java Program Demonstrate poll()
// method of LinkedBlockingQueue
import java.util.concurrent.LinkedBlockingQueue;
public class GFG {
public void pollingMethod()
{
// define capacity of LinkedBlockingQueue
int capacityOfQueue = 5;
// create object of LinkedBlockingQueue
LinkedBlockingQueue<Employee> linkedQueue
= new LinkedBlockingQueue<Employee>(capacityOfQueue);
// Add element to LinkedBlockingQueue
Employee emp1 = new Employee("Ravi", "Tester", "39000");
Employee emp2 = new Employee("Sanjeet", "Manager", "98000");
// Add Employee Objects to linkedQueue
linkedQueue.add(emp1);
linkedQueue.add(emp2);
// remove elements from the queue
// and follow this process again and again
// until the queue becomes empty
while (linkedQueue.size() != 0) {
// Remove Employee item from LinkedBlockingQueue
Employee removedEmp = linkedQueue.poll();
// print removedItem
System.out.println("Removed Item is :");
System.out.println("Employee Name - " + removedEmp.name);
System.out.println("Employee Position - " + removedEmp.position);
System.out.println("Employee Salary - " + removedEmp.salary);
// find size of linkedQueue
int size = linkedQueue.size();
// print remaining capacity value
System.out.println("\nSize of list :" + size + "\n");
}
// Now size of Queue is Zero
// Now try to Poll more items
// Remove Employee item from LinkedBlockingQueue
Employee removedEmp = linkedQueue.poll();
// print removedItem
// size is zero so removedItem is null
System.out.println("Removed Item is : " + removedEmp);
}
// create an Employee Object with name,
// position and salary as an attribute
public class Employee {
public String name;
public String position;
public String salary;
Employee(String name, String position, String salary)
{
this.name = name;
this.position = position;
this.salary = salary;
}
@Override
public String toString()
{
return "Employee [name=" + name + ", position="
+ position + ", salary=" + salary + "]";
}
}
// Main Method
public static void main(String[] args)
{
GFG gfg = new GFG();
gfg.pollingMethod();
}
}
Removed Item is : Employee Name - Ravi Employee Position - Tester Employee Salary - 39000 Size of list :1 Removed Item is : Employee Name - Sanjeet Employee Position - Manager Employee Salary - 98000 Size of list :0 Removed Item is : null
poll(long timeout, TimeUnit unit)
LinkedBlockingQueue的poll(long timeout,TimeUnit unit)方法通过从队列中删除该元素来返回LinkedBlockingQueue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。
以下示例程序旨在说明LinkedBlockingQueue类的poll(长时间超时,TimeUnit单位)方法:
示例1:使用poll()方法从LinkedBlockingQueue中删除元素,其中LinkedBlockingQueue包含名称列表。
// Java program to demonstrate
// poll(long timeout, TimeUnit unit)
// method of LinkedBlockingQueue
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
public class GFG {
public static void main(String[] args)
throws InterruptedException
{
// define capacity of LinkedBlockingQueue
int capacityOfQueue = 4;
// create object of LinkedBlockingQueue
LinkedBlockingQueue<String> linkedQueue
= new LinkedBlockingQueue<String>(capacityOfQueue);
// Add element to LinkedBlockingQueue
linkedQueue.add("Ravi");
linkedQueue.add("Suraj");
linkedQueue.add("Harsh");
// print elements of queue
System.out.println("Items in Queue are " + linkedQueue);
// Try to poll elements from linkedQueue
// using poll(long timeout, TimeUnit unit) method
System.out.println("Removing item From head: "
+ linkedQueue.poll(5, TimeUnit.SECONDS));
// print queue details
System.out.println("Now Queue Contains" + linkedQueue);
// using poll(long timeout, TimeUnit unit) method
System.out.println("Removing item From head: "
+ linkedQueue.poll(5, TimeUnit.SECONDS));
// print queue details
System.out.println("Now Queue Contains" + linkedQueue);
// using poll(long timeout, TimeUnit unit) method
System.out.println("Removing item From head: "
+ linkedQueue.poll(5, TimeUnit.SECONDS));
// print queue details
System.out.println("Now Queue Contains" + linkedQueue);
// using poll(long timeout, TimeUnit unit) method
System.out.println("Removing item From head: "
+ linkedQueue.poll(5, TimeUnit.SECONDS));
// print queue details
System.out.println("Now Queue Contains" + linkedQueue);
}
}
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[]
参考:
- https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/LinkedBlockingQueue.html#poll–
- https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/LinkedBlockingQueue.html#poll-long-java.util.concurrent.TimeUnit-
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注:本文由纯净天空筛选整理自AmanSingh2210大神的英文原创作品 LinkedBlockingQueue poll() method in Java。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。