Java PriorityBlockingQueue toArray()用法及代码示例

toArray()

PriorityBlockingQueue的toArray方法用于以适当的顺序创建一个数组，该数组具有与此PriorityBlockingQueue相同的元素。实际上，此方法将所有元素从PriorityBlockingQueue复制到新数组。此方法充当数组和PriorityBlockingQueue之间的桥梁。

用法:

public Object[] toArray()

返回值：此方法返回一个包含PriorityBlockingQueue元素的数组。

下面的程序说明PriorityBlockingQueue类的toArray()方法：

示例1:程序演示在PriorityBlockingQueue上使用toArray()方法从包含数字的PriorityBlockingQueue创建数字数组。

// Java Program Demonstrate toArray() 
// method of PriorityBlockingQueue 
  
import java.util.concurrent.PriorityBlockingQueue; 
public class GFG { 
  
    public static void main(String[] args) 
    { 
        // define capacity of PriorityBlockingQueue 
        int capacityOfQueue = 5; 
  
        // create object of PriorityBlockingQueue 
        PriorityBlockingQueue<Integer> PrioQueue 
            = new PriorityBlockingQueue<Integer>(capacityOfQueue); 
  
        // Add numbers to PriorityBlockingQueue 
        PrioQueue.offer(35658786); 
        PrioQueue.offer(5278367); 
        PrioQueue.offer(74381793); 
        PrioQueue.offer(87625142); 
  
        // create an array of elements of PriorityBlockingQueue 
        Object[] array = PrioQueue.toArray(); 
  
        // print elements of array 
        System.out.println("Array Contains:"); 
        for (Object i : array) { 
            System.out.print(i + " "); 
        } 
    } 
}

输出：

Array Contains:
5278367 35658786 74381793 87625142

示例2:程序演示在PriorityBlockingQueue上使用toArray()方法从包含字符串值的PriorityBlockingQueue创建字符串数组。

// Java Program Demonstrate toArray() 
// method of PriorityBlockingQueue 
  
import java.util.concurrent.PriorityBlockingQueue; 
import java.util.*; 
  
public class GFG { 
    public static void main(String[] args) 
    { 
  
        // define capacity of PriorityBlockingQueue 
        int capacityOfQueue = 5; 
  
        // create object of PriorityBlockingQueue which contains 
        // name of students 
        PriorityBlockingQueue<String> names 
            = new PriorityBlockingQueue<String>(capacityOfQueue); 
  
        // Add names of students of girls college 
        names.offer("Joyita"); 
        names.offer("Bristi"); 
        names.offer("Riya"); 
  
        // Create a array by calling toArray() method 
        Object[] array = names.toArray(); 
  
        // Print List of names 
        System.out.println("Queue is " + names); 
  
        // Print elements of array 
        System.out.println("The array created by toArray() is:"); 
        for (Object i : array) { 
            System.out.println(i + " "); 
        } 
    } 
}

输出：

Queue is [Bristi, Joyita, Riya]
The array created by toArray() is:
Bristi 
Joyita 
Riya

toArray(T[] a)

PriorityBlockingQueue的toArray(T [] a)方法用于按正确顺序返回包含与该PriorityBlockingQueue元素相同的元素的数组。此方法仅在一种情况下与toArray()不同。如果PriorityBlockingQueue大小小于或等于传递的数组，则返回的数组的类型与参数中传递的数组的类型相同。否则，将分配一个与指定数组相同类型的新数组，并且该数组的大小等于此队列的大小。此方法充当数组和集合之间的桥梁。

用法:

public <T> T[] toArray(T[] a)

参数：此方法将数组作为参数，如果队列足够大，则要将队列的所有元素都复制到该数组中。否则，将为它分配一个具有相同运行时类型的新数组。

返回值：此方法返回一个包含此队列中所有元素的数组。

异常此方法引发以下异常：

ArrayStoreException：当传递的数组与PriorityBlockingQueue的元素类型不同时。
NullPointerException ：如果传递的数组为Null。

下面的程序说明PriorityBlockingQueue类的toArray(T [] a)方法：

示例1:该程序演示PriorityBlockingQueue上的toArray(T [] a)方法。

// Java Program Demonstrate toArray(T[] a) 
// method of PriorityBlockingQueue 
  
import java.util.concurrent.PriorityBlockingQueue; 
import java.util.concurrent.TimeUnit; 
  
public class GFG { 
  
    public static void main(String[] args) 
        throws InterruptedException 
    { 
        // define capacity of PriorityBlockingQueue 
        int capacityOfQueue = 3; 
  
        // create object of PriorityBlockingQueue 
        PriorityBlockingQueue<String> PrioQueue 
            = new PriorityBlockingQueue<String>(capacityOfQueue); 
  
        // Add names of students of girls college 
        PrioQueue.offer("Joyi"); 
        PrioQueue.offer("Rani"); 
        PrioQueue.offer("Riya"); 
  
        // Creating the array 
        String[] array = new String[capacityOfQueue]; 
  
        // Calling toArray(T[] a) method 
        Object[] ReturnArray = PrioQueue.toArray(array); 
  
        // Print queue 
        System.out.println("Queue is " + PrioQueue); 
  
        // Print elements of array passed as parameter 
        System.out.println(); 
        System.out.println("The array passed to toArray() is:"); 
        for (Object i : array) { 
            System.out.println(i); 
        } 
  
        // Print elements of array retuned by method toArray() 
        System.out.println(); 
        System.out.println("The array retuned by toArray() is:"); 
        for (Object i : ReturnArray) { 
            System.out.println(i); 
        } 
    } 
}

输出：

Queue is [Joyi, Rani, Riya]

The array passed to toArray() is:
Joyi
Rani
Riya

The array retuned by toArray() is:
Joyi
Rani
Riya

示例2:演示由PriorityBlockingQueue的toArray(T [] a)方法引发的异常的程序。

// Java Program Demonstrate toArray(T[] a) 
// method of PriorityBlockingQueue 
  
import java.util.concurrent.PriorityBlockingQueue; 
import java.util.concurrent.TimeUnit; 
  
public class GFG { 
  
    public static void main(String[] args) 
        throws InterruptedException 
    { 
        // define capacity of PriorityBlockingQueue 
        int capacityOfQueue = 3; 
  
        // create object of PriorityBlockingQueue 
        PriorityBlockingQueue<String> PrioQueue 
            = new PriorityBlockingQueue<String>(capacityOfQueue); 
  
        // Add names of students of girls college 
        PrioQueue.offer("Joyi"); 
        PrioQueue.offer("Rani"); 
        PrioQueue.offer("Riya"); 
  
        // Creating the array with null value 
        String[] array = null; 
  
        try { 
            // Calling toArray(T[] a) method 
            Object[] ReturnArray = PrioQueue.toArray(array); 
        } 
        catch (Exception e) { 
            System.out.println("Exception thrown:" + e); 
        } 
    } 
}

输出：

Exception thrown:java.lang.NullPointerException

参考：

相关用法

注：本文由纯净天空筛选整理自AmanSingh2210大神的英文原创作品 PriorityBlockingQueue toArray() method in Java。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。