Java中的 DelayQueue toArray() 方法及示例

DelayQueue 的toArray()方法用于返回一个包含 DelayQueue 中所有元素的数组。数组中的元素没有任何特定的顺序。
句法：

public Object[] toArray ()
           or
public T[] toArray (T[] a)

参数：此方法要么不接受参数，要么接受一个数组T[] a 作为参数，如果它足够大，则该数组是要存储列表元素的数组；否则，将为此目的分配相同运行时类型的新数组。
返回值：该函数返回一个包含此列表中所有元素的数组。
异常：此方法的第一次重载不会引发异常。但是，第二个重载会引发以下异常：

• ArrayStoreException：如果指定数组的运行时类型不是此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。

下面的程序说明了 DelayQueue.toArray() 方法：
方案一：

Java

// 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 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 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}]

方案二：

Java

// 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 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 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}]