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<DelayObject> DQ
= new DelayQueue<DelayObject>();
// 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<DelayObject> DQ
= new DelayQueue<DelayObject>();
// 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
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注:本文由纯净天空筛选整理自ProgrammerAnvesh大神的英文原创作品 DelayQueue 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。