Java BlockingDeque pollFirst()方法及示例
BlockingDeque 的 pollFirst() 方法返回Deque容器中的前一个元素,并将其删除。如果容器是空的,它返回 null 。
语法
public E pollFirst()
参数: 该方法不接受任何参数。
返回: 如果Deque容器不是空的,该方法返回该容器中的前部元素,并删除该元素。如果容器是空的,它返回null。
注意 : BlockingDeque 的pollFirst()方法已经从Java中的LinkedBlockingDeque类继承。
以下程序说明了BlockingDeque的pollFirst()方法。
程序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);
}
}
输出。
Blocking Deque: [74381793, 5278367, 35658786, 7855642]
Front element in Deque: 74381793
Blocking Deque: [5278367, 35658786, 7855642]
程序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());
}
}
输出。
Blocking Deque: [7855642, 35658786, 5278367, 74381793]
Front element in Deque: null
参考: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingDeque.html#pollFirst(long, %20java.util.concurrent.TimeUnit)。