极客教程Java DelayQueue toArray()方法及示例
DelayQueue的 toArray() 方法是用来返回一个包含DelayQueue中所有元素的数组。这些元素在数组中没有任何特定的顺序。
语法：
public Object[] toArray ()
或者
public T[] toArray (T[] a)
参数： 该方法要么不接受任何参数，要么接受一个数组 T[] a作为参数，如果该数组足够大的话，就将列表中的元素存储到该数组中；否则，将为此目的分配一个相同运行时类型的新数组。
返回值： 该函数返回 一个 包含该列表中所有元素的 数组 。
异常： 该方法的第一个重载没有抛出异常。然而，第二个重载会抛出以下异常：
- ArrayStoreException： 如果指定数组的运行时类型不是这个队列中每个元素的运行时类型的超类型。
- NullPointerException： 如果指定的数组为空。
以下程序说明了DelayQueue.toArray()方法：
程序1：
// Java Program Demonstrate DelayQueue toArray() 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 queue
System.out.println("DelayQueue: "
+ DQ);
// Get the array of the elements
// of the ArrayList
// using toArray() method
Object[] arr = DQ.toArray();
// print the array elements
System.out.println("Elements of DelayQueue"
+ " as Array: "
+ Arrays.toString(arr));
}
}
输出
DelayQueue: [
{ A, time=1546842694862},
{ B, time=1546842694863},
{ C, time=1546842694864},
{ D, time=1546842694865}]
Elements of DelayQueue as Array: [
{ A, time=1546842694862},
{ B, time=1546842694863},
{ C, time=1546842694864},
{ D, time=1546842694865}]
程序2：
// Java Program Demonstrate DelayQueue toArray() 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 queue
System.out.println("DelayQueue: "
+ DQ);
// Get the array of the elements
// of the DelayQueue
// using toArray(T[]) method
Delayed arr[] = new Delayed[DQ.size()];
arr = DQ.toArray(arr);
// print the array elements
System.out.println("Elements of ArrayList"
+ " as Array: "
+ Arrays.toString(arr));
}
}
输出
DelayQueue: [
{ A, time=1546842699503},
{ B, time=1546842699504},
{ C, time=1546842699505},
{ D, time=1546842699506}]
Elements of ArrayList as Array: [
{ A, time=1546842699503},
{ B, time=1546842699504},
{ C, time=1546842699505},
{ D, time=1546842699506}]