本文共 3787 字，大约阅读时间需要 12 分钟。
DelayQueue的poll()方法用于检索DelayQueue的头部。此方法还从DelayQueue中删除头。因此，当调用poll方法时，DelayQueue的大小将减小1。
用法:
public E poll ()
参数：
此方法不接受任何参数。
返回值：
此方法返回DelayQueue的头部，并将其从此DelayQueue中删除。
异常：
NullPointerException ：如果head不存在，则此函数将返回null。
下面的程序来说明Java中的DelayQueue poll()：
例：
// Java Program Demonstrate DelayQueue poll() method
import java.util.concurrent.*;
import java.util.*;
// The DelayObject for DelayQueue
// It must implement Delayed and
// its getDelay() and compareTo() method
class DelayObject implements Delayed {
private String name;
private long time;
// Contructor of DelayObject
public DelayObject(String name, long delayTime)
{
this.name = name;
this.time = System.currentTimeMillis()
+ delayTime;
}
// Implementing getDelay() method of Delayed
@Override
public long getDelay(TimeUnit unit)
{
long diff = time - System.currentTimeMillis();
return unit.convert(diff, TimeUnit.MILLISECONDS);
}
// Implementing compareTo() method of Delayed
@Override
public int compareTo(Delayed obj)
{
if (this.time < ((DelayObject)obj).time) {
return -1;
}
if (this.time > ((DelayObject)obj).time) {
return 1;
}
return 0;
}
// Implementing toString() method of Delayed
@Override
public String toString()
{
return "\n{"
+ " " + name + ", time=" + time + "}";
}
}
// Driver Class
public class GFG {
public static void main(String[] args) throws InterruptedException
{
// create object of DelayQueue
// using DelayQueue() constructor
BlockingQueue DQ
= new DelayQueue();
// Add numbers to end of DelayQueue
// using add() method
DQ.add(new DelayObject("A", 1));
DQ.add(new DelayObject("B", 2));
DQ.add(new DelayObject("C", 3));
DQ.add(new DelayObject("D", 4));
// Print delayqueue
System.out.println("Original DelayQueue: "
+ DQ + "\n");
// Print size of original DelayQueue
System.out.println("Original DelayQueue size: "
+ DQ.size() + "\n");
// poll() method for returning head of the DelayQueue
System.out.println("Head of the DelayQueue: "
+ DQ.poll());
// print DelayQueue size after poll method
System.out.println("\nAfter poll() method, DelayQueue size: "
+ DQ.size());
}
}
输出：
Original DelayQueue: [
{ A, time=1545817370442},
{ B, time=1545817370443},
{ C, time=1545817370444},
{ D, time=1545817370445}]
Original DelayQueue size: 4
Head of the DelayQueue:
{ A, time=1545817370442}
After poll() method, DelayQueue size: 3
例：
// Java Program Demonstrate DelayQueue poll() method
import java.util.concurrent.*;
import java.util.*;
// The DelayObject for DelayQueue
// It must implement Delayed and
// its getDelay() and compareTo() method
class DelayObject implements Delayed {
private String name;
private long time;
// Contructor of DelayObject
public DelayObject(String name, long delayTime)
{
this.name = name;
this.time = System.currentTimeMillis()
+ delayTime;
}
// Implementing getDelay() method of Delayed
@Override
public long getDelay(TimeUnit unit)
{
long diff = time - System.currentTimeMillis();
return unit.convert(diff, TimeUnit.MILLISECONDS);
}
// Implementing compareTo() method of Delayed
@Override
public int compareTo(Delayed obj)
{
if (this.time < ((DelayObject)obj).time) {
return -1;
}
if (this.time > ((DelayObject)obj).time) {
return 1;
}
return 0;
}
// Implementing toString() method of Delayed
@Override
public String toString()
{
return "\n{"
+ " " + name + ", time=" + time + "}";
}
}
// Driver Class
public class GFG {
public static void main(String[] args) throws InterruptedException
{
// create object of DelayQueue
// using DelayQueue() constructor
BlockingQueue DQ
= new DelayQueue();
// Print size of original DelayQueue
System.out.println("Original DelayQueue size: "
+ DQ.size() + "\n");
// poll() method for returning head of the DelayQueue
System.out.println("Head of the DelayQueue: "
+ DQ.poll());
}
}
输出：
Original DelayQueue size: 0
Head of the DelayQueue: null
转载地址：http://pqltx.baihongyu.com/