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ConcurrentLinkedQueue toArray() Method in Java

Last Updated : 26 Nov, 2018

1. toArray() : The toArray() method of ConcurrentLinkedQueue is used to returns an array of the same elements as that of the ConcurrentLinkedQueue in proper sequence. Basically, it copies all the element from a ConcurrentLinkedQueue to a new array. This method behaves as a bridge between array and ConcurrentLinkedQueue. Syntax:

   public Object[] toArray()

   Returns: The method returns an array containing the elements similar to the ConcurrentLinkedQueue. Below programs illustrate the java.util.concurrent.ConcurrentLinkedQueue.toArray() method. Example 1: Java

   // Java Program Demonstrate toArray()
   // method of ConcurrentLinkedQueue
   
   import java.util.concurrent.ConcurrentLinkedQueue;
   
   public class GFG {
   
       public static void main(String[] args)
       {
           // create object of ConcurrentLinkedQueue
           ConcurrentLinkedQueue<Integer> queue
               = new ConcurrentLinkedQueue<Integer>();
   
           // Add element to ConcurrentLinkedQueue
           queue.add(2300);
           queue.add(1322);
           queue.add(8945);
           queue.add(6512);
   
           // print queue details
           System.out.println("Queue Contains " + queue);
   
           // apply toArray() method on queue
           Object[] array = queue.toArray();
   
           // Print elements of array
           System.out.println("The array contains:");
           for (Object i : array) {
               System.out.print(i + "\t");
           }
       }
   }
   

   Output:

   Queue Contains [2300, 1322, 8945, 6512]
   The array contains:
   2300    1322    8945    6512
   

   Example 2: Java

   // Java Program Demonstrate toArray()
   // method of ConcurrentLinkedQueue
   
   import java.util.concurrent.ConcurrentLinkedQueue;
   
   public class GFG {
       public static void main(String args[])
       {
           // Creating a ConcurrentLinkedQueue
           ConcurrentLinkedQueue<String>
               queue = new ConcurrentLinkedQueue<String>();
   
           // elements into the Queue
           queue.add("Welcome");
           queue.add("To");
           queue.add("Jungle");
   
           // Displaying the ConcurrentLinkedQueue
           System.out.println("The ConcurrentLinkedQueue: "
                              + queue);
   
           // Creating the array and using toArray()
           Object[] arr = queue.toArray();
   
           System.out.println("The array is:");
           for (int j = 0; j < arr.length; j++)
               System.out.println(arr[j]);
       }
   }
   

   Output:

   The ConcurrentLinkedQueue: [Welcome, To, Jungle]
   The array is:
   Welcome
   To
   Jungle
   

2. toArray(T[] a) : The toArray(T[] a) method of ConcurrentLinkedQueue is used to an array containing the same elements as that of this ConcurrentLinkedQueue in proper sequence. This method differs from toArray() in only one condition. The type of the returned array is the same as the passed array in the parameter, if the ConcurrentLinkedQueue size is less than or equal to the passed array. Otherwise, a new array is allocated with the type same as the specified array and size of the array is equal to the size of this queue. This method behaves as a bridge between array and collections. Syntax:

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

   Parameter: This method takes array as parameter into which all of the elements of the queue are to be copied, if it is big enough. Otherwise, a new array of the same runtime type is allocated to this. Returns: This method returns array containing the elements similar to the ConcurrentLinkedQueue. Exception: This method throws following exceptions:
   • ArrayStoreException: When the passed array is of the different type from the type of elements of ConcurrentLinkedQueue.
   • NullPointerException: If the passed array is Null.
   Below programs illustrate the java.util.concurrent.ConcurrentLinkedQueue.toArray(T[] a) method. Example 1: Java

   // Java Program Demonstrate toArray()
   // method of ConcurrentLinkedQueue
   
   import java.util.concurrent.ConcurrentLinkedQueue;
   
   public class GFG {
   
       public static void main(String[] args)
       {
           // create object of ConcurrentLinkedQueue
           ConcurrentLinkedQueue<String> queue
               = new ConcurrentLinkedQueue<String>();
   
           // elements into the Queue
           queue.add("Welcome");
           queue.add("To");
           queue.add("Jungle");
   
           // print queue details
           System.out.println("Queue Contains " + queue);
   
           // the array to pass in toArray()
           // array has size equal to size of ConcurrentLinkedQueue
           String[] passArray = new String[queue.size()];
   
           // Calling toArray(T[] a) method
           Object[] array = queue.toArray(passArray);
   
           // Print elements of passed array
           System.out.println("\nThe array passed :");
           for (String i : passArray) {
               System.out.print(i + " ");
           }
   
           System.out.println();
   
           // Print elements of returned array
           System.out.println("\nThe array returned :");
           for (Object i : array) {
               System.out.print(i + " ");
           }
       }
   }
   

   Output:

   Queue Contains [Welcome, To, Jungle]
   
   The array passed :
   Welcome To Jungle 
   
   The array returned :
   Welcome To Jungle
   

   Example 2: To show ArrayStoreException Java

   // Java Program Demonstrate toArray()
   // method of ConcurrentLinkedQueue
   
   import java.util.concurrent.ConcurrentLinkedQueue;
   
   public class GFG {
   
       public static void main(String[] args)
       {
           // create object of ConcurrentLinkedQueue
           ConcurrentLinkedQueue<Integer> queue
               = new ConcurrentLinkedQueue<Integer>();
   
           // Add element to ConcurrentLinkedQueue
           queue.add(2323);
           queue.add(2472);
           queue.add(4235);
           queue.add(1242);
   
           // the array to pass in toArray()
           // array has size equal to size of ConcurrentLinkedQueue
           String[] passArray = new String[queue.size()];
   
           // Calling toArray(T[] a) method
           try {
               Object[] array = queue.toArray(passArray);
           }
           catch (ArrayStoreException e) {
               System.out.println("Exception: " + e);
           }
       }
   }
   

   Output:

   Exception: java.lang.ArrayStoreException: java.lang.Integer
   

   Example 2: To show NullPointerException Java

   // Java Program Demonstrate toArray()
   // method of ConcurrentLinkedQueue
   
   import java.util.concurrent.ConcurrentLinkedQueue;
   
   public class GFG {
   
       public static void main(String[] args)
       {
           // create object of ConcurrentLinkedQueue
           ConcurrentLinkedQueue<Integer> queue
               = new ConcurrentLinkedQueue<Integer>();
   
           // Add element to ConcurrentLinkedQueue
           queue.add(2323);
           queue.add(2472);
           queue.add(4235);
           queue.add(1242);
   
           // the array to pass
           String[] passArray = null;
   
           // Calling toArray(T[] a) method
           try {
               Object[] array = queue.toArray(passArray);
           }
           catch (NullPointerException e) {
               System.out.println("Exception: " + e);
           }
       }
   }
   

   Output:

   Exception: java.lang.NullPointerException
   

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