LinkedBlockingQueue中有两种poll（）方法。
null
投票
这个 投票 方法 LinkedBlockingQueue 通过从队列中删除LinkedBlockingQueue的元素，返回该元素的头。可以说，这个方法从这个LinkedBlockingQueue的头部检索并移除元素。如果队列为空，则poll方法返回null。
语法：
public E poll()
返回值： 此方法从这个LinkedBlockingQueue的头部检索并删除元素。如果队列为空，则返回null。
下面的程序演示了LinkedBlockingQueue类的poll（）方法：
项目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); } } |
输出：
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]
项目2： 正在从包含员工列表的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( "Size of list :" + size + "" ); } // 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(); } } |
输出：
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
轮询（长超时，时间单位）
这个 轮询（长超时，时间单位） 方法 LinkedBlockingQueue 通过从队列中删除LinkedBlockingQueue的元素，返回该元素的头。可以说，这个方法从这个LinkedBlockingQueue的头部检索并移除元素。如果队列为空，则poll（）方法将等到指定的时间，元素才可用。
语法：
public E poll(long timeout, TimeUnit unit) throws
参数： 此方法采用两个强制参数：
- 暂停 –等待的时间，以单位为单位。
- 单元 –超时参数的时间单位。
返回值： 此方法检索并从此LinkedBlockingQueue的头中删除元素，如果在元素可用之前经过指定的等待时间，则为null。
例外 这个方法抛出 中断异常 如果方法在等待元素可用时中断。
下面的程序演示了LinkedBlockingQueue类的轮询（长超时，时间单位）方法：
项目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); } } |
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[]
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-长爪哇。util。同时发生的时间单位-
© 版权声明
文章版权归作者所有，未经允许请勿转载。
THE END
![关于”PostgreSQL错误：关系[表]不存在“问题的原因和解决方案-yiteyi-C++库](https://www.yiteyi.com/wp-content/themes/zibll/img/thumbnail.svg)
