Java 中的 DelayQueue peek()方法，带示例
原文:https://www . geeksforgeeks . org/delay queue-peek-method-in-Java-with-examples/
DelayQueue 的 peek() 方法用于检索 DelayQueue 的头，但不会将其移除，就像 poll()方法中头从 DelayQueue 中移除一样。
语法:
public E peek ()
参数: 此方法不接受任何参数。
返回: 这个方法返回延迟队列的头，并且不从这个延迟队列中删除它。
异常: 空指针异常:如果头部不存在，该函数将返回空。
下面用 Java 编程来说明 DelayQueue peek():
例 1:
Java 语言(一种计算机语言，尤用于创建网站)
// Java Program Demonstrate DelayQueue peek() 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;
// Constructor 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");
// peek() method for returning head of the DelayQueue
System.out.println("Head of the DelayQueue: "
+ DQ.peek());
// print DelayQueue
System.out.println("\nAfter peek() method, DelayQueue: "
+ DQ);
}
}
Output:
Original DelayQueue: [
{ A, time=1545817334485},
{ B, time=1545817334486},
{ C, time=1545817334487},
{ D, time=1545817334488}]
Head of the DelayQueue:
{ A, time=1545817334485}
After peek() method, DelayQueue: [
{ A, time=1545817334485},
{ B, time=1545817334486},
{ C, time=1545817334487},
{ D, time=1545817334488}]
例 2:
Java 语言(一种计算机语言，尤用于创建网站)
// Java Program Demonstrate DelayQueue peek() 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;
// Constructor 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));
// Print delayqueue
System.out.println("Original DelayQueue: "
+ DQ + "\n");
// removing all elements
DQ.clear();
// peek() method for returning head of the DelayQueue
System.out.println("Head of the DelayQueue: " + DQ.peek());
}
}
Output:
Original DelayQueue: [
{ A, time=1545817342666},
{ B, time=1545817342667}]
Head of the DelayQueue: null
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