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LinkedBlockingQueue toArray() method in Java
  • Last Updated : 26 Nov, 2018

toArray()

The toArray method of LinkedBlockingQueue is used to create an array having the same elements as that of this LinkedBlockingQueue, in proper sequence. Actually, this method copies all the element from the LinkedBlockingQueue to a new array. This method behaves as a bridge between array and LinkedBlockingQueue.

Syntax:

public Object[] toArray()

Return Value: This method returns an array which contains the elements of LinkedBlockingQueue.

Below programs illustrates toArray() method of LinkedBlockingQueue class:

Program 1:






// Java Program Demonstrate toArray()
// method of LinkedBlockingQueue
  
import java.util.concurrent.LinkedBlockingQueue;
  
public class GFG {
  
    public static void main(String[] args)
    {
        // define capacity of LinkedBlockingQueue
        int capacityOfQueue = 50;
  
        // create object of LinkedBlockingQueue
        LinkedBlockingQueue<Integer> linkedQueue
            = new LinkedBlockingQueue<Integer>(capacityOfQueue);
  
        // Add element to LinkedBlockingQueue
        linkedQueue.add(2300);
        linkedQueue.add(1322);
        linkedQueue.add(8945);
        linkedQueue.add(6512);
  
        // print linkedQueue details
        System.out.println("Queue Contains "
                           + linkedQueue);
  
        // apply toArray() method on linkedQueue
        Object[] array = linkedQueue.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

Program 2:




// Java Program Demonstrate toArray()
// method of LinkedBlockingQueue
  
import java.util.concurrent.LinkedBlockingQueue;
  
public class GFG {
    public static void main(String[] args)
    {
        // define capacity of LinkedBlockingQueue
        int capacityOfQueue = 5;
  
        // create object of LinkedBlockingQueue
        LinkedBlockingQueue<String> linkedQueue
            = new LinkedBlockingQueue<String>(capacityOfQueue);
  
        // Add 5 elements to ArrayBlockingQueue
        linkedQueue.offer("User");
        linkedQueue.offer("Employee");
        linkedQueue.offer("Manager");
        linkedQueue.offer("Analyst");
        linkedQueue.offer("HR");
  
        // apply toArray() method on linkedQueue
        Object[] array = linkedQueue.toArray();
  
        // Print elements of array
        System.out.println("The array contains:");
        for (Object i : array) {
            System.out.print(i + " ");
        }
    }
}


Output:

The array contains:
User Employee Manager Analyst HR

toArray(T[] a)

The toArray(T[] a) method of LinkedBlockingQueue is used to return an array containing the same elements as that of this LinkedBlockingQueue, 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 LinkedBlockingQueue 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 an 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.

Return Value: This method returns an array containing all of the elements in this queue.

Exception This method throws following exceptions:



  • ArrayStoreException: When the passed array is of the different type from the type of elements of LinkedBlockingQueue.
  • NullPointerException: If the passed array is Null.

Below programs illustrates toArray(T[] a) method of LinkedBlockingQueue class:

Program 1




// Java program to demonstrate
// toArray(T[] a) method
// method of LinkedBlockingQueue
  
import java.util.concurrent.LinkedBlockingQueue;
  
public class GFG {
  
    public static void main(String[] args)
    {
        // define capacity of LinkedBlockingQueue
        int capacityOfQueue = 10;
  
        // create object of LinkedBlockingQueue
        LinkedBlockingQueue<String> linkedQueue
            = new LinkedBlockingQueue<String>(capacityOfQueue);
  
        // Add 5 elements to ArrayBlockingQueue
        linkedQueue.offer("Sonali");
        linkedQueue.offer("Sonam");
        linkedQueue.offer("Kajal");
        linkedQueue.offer("Komal");
  
        // Print queue
        System.out.println("Queue Contains : " + linkedQueue);
  
        // the array to pass in toArray()
        // array has size equal to size of linkedQueue
        String[] passArray = new String[linkedQueue.size()];
  
        // Calling toArray(T[] a) method
        Object[] array = linkedQueue.toArray(passArray);
  
        // Print elements of passed array
        System.out.println("\nThe array passed :");
        for (Object i : passArray) {
            System.out.print(i + "\t");
        }
  
        System.out.println();
  
        // Print elements of returned array
        System.out.println("\nThe array retuned :");
        for (Object i : array) {
            System.out.print(i + "\t");
        }
    }
}


Output:

Queue Contains : [Sonali, Sonam, Kajal, Komal]

The array passed :
Sonali    Sonam    Kajal    Komal    

The array retuned :
Sonali    Sonam    Kajal    Komal

Program 2: Passing different type of array in toArray() from the type of element LinkedBlockingQueue contains. The toArray() method will hence throw exception ArrayStoreException.




// Java Program Demonstrate
// toArray()
// method Exceptions.
  
import java.util.concurrent.LinkedBlockingQueue;
  
public class GFG {
  
    public static void main(String[] args)
        throws InterruptedException
    {
        // define capacity of LinkedBlockingQueue
        int capacityOfQueue = 4;
  
        // create object of LinkedBlockingQueue
        LinkedBlockingQueue<Integer>
            linkedQueue = new LinkedBlockingQueue<Integer>(capacityOfQueue);
  
        // add elements to queue
        linkedQueue.put(46541);
        linkedQueue.put(44648);
        linkedQueue.put(45654);
  
        // create a array of Strings
        String[] arr = {};
  
        // apply toArray method and Pass array of String
        // as parameter to toArray method
        try {
            // LinkedBlockingQueue has type Integer but we are passing
            // String Type array so toArray method will throw
            // Exception
            String[] array = linkedQueue.toArray(arr);
  
            // print elements of queue
            System.out.println("Items in Queue are " + array);
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}


Output:

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

Program 3: Passing null array in toArray(). Hence toArray() method will throw NullPointerException.




// Java program to demonstrate
// toArray() method Exceptions.
  
import java.util.concurrent.LinkedBlockingQueue;
  
public class GFG {
  
    public static void main(String[] args)
        throws InterruptedException
    {
        // define capacity of LinkedBlockingQueue
        int capacityOfQueue = 4;
  
        // create object of LinkedBlockingQueue
        LinkedBlockingQueue<String>
            linkedQueue = new LinkedBlockingQueue<String>(capacityOfQueue);
  
        // add elements to queue
        linkedQueue.put("aman");
        linkedQueue.put("khan");
        linkedQueue.put("Prakash");
  
        // create a array of Strings
        String[] arr = null;
  
        // apply toArray method and Pass array of String
        // as parameter to toArray method
        try {
  
            /// we are passing array with null values
            String[] array = linkedQueue.toArray(arr);
  
            // print elements of queue
            System.out.println("Items in Queue are " + array);
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}


Output:

Exception: java.lang.NullPointerException

Reference:

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