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PriorityQueue toArray() Method in Java

  • Difficulty Level : Hard
  • Last Updated : 10 Dec, 2018
  1. The java.util.PriorityQueue.toArray() method in Java is used to form an array of the same elements as that of the Priority Queue. Basically, it copies all the element from a priority queue to a new array.

    Syntax:

    Object[] arr = Priority_Queue.toArray()

    Parameters: The method does not take any parameters.

    Return Value: The method returns an array containing the elements similar to the priority queue.

    Below programs illustrate the java.util.PriorityQueue.toArray() method.
    Program 1:




    // Java code to illustrate toArray()
    import java.util.*;
      
    public class PriorityQueueDemo {
        public static void main(String args[])
        {
            // Creating an empty PriorityQueue
            PriorityQueue<String> queue = new PriorityQueue<String>();
      
            // Use add() method to add elements into the Queue
            queue.add("Welcome");
            queue.add("To");
            queue.add("Geeks");
            queue.add("For");
            queue.add("Geeks");
      
            // Displaying the PriorityQueue
            System.out.println("The PriorityQueue: " + 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 PriorityQueue: [For, Geeks, To, Welcome, Geeks]
    The array is:
    For
    Geeks
    To
    Welcome
    Geeks
    

    Program 2:




    // Java code to illustrate toArray()
    import java.util.*;
      
    public class PriorityQueueDemo {
        public static void main(String args[])
        {
            // Creating an empty PriorityQueue
            PriorityQueue<Integer> queue = new PriorityQueue<Integer>();
      
            // Use add() method to add elements into the Queue
            queue.add(10);
            queue.add(15);
            queue.add(30);
            queue.add(20);
            queue.add(5);
            queue.add(25);
      
            // Displaying the PriorityQueue
            System.out.println("The PriorityQueue: " + 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 PriorityQueue: [5, 10, 25, 20, 15, 30]
    The array is:
    5
    10
    25
    20
    15
    30
    
  2. The java.util.PriorityQueue.toArray(arr[]) method in Java is used to form an array of the same elements as that of the Priority Queue. Basically, it copies all the element from a priority queue to a new array. It creates multiple arrays, unlike the previous method without parameters. This method copies all of the elements into the arr[].
    Syntax:
    Object[] arr1 = Priority_Queue.toArray(arr[])

    Parameters: The method accepts one parameter arr[] into which all of the elements of the queue are to be copied.

    Return Value: The method returns an array containing the elements similar to the priority queue.

      Exception: The method might throw two types of exception:

    • ArrayStoreException: When the mentioned array is of the different type and is not able to compare with the elements mentioned in the queue.
    • NullPointerException: If the array is Null, then this exception is thrown.

    Below program illustrates the working of the java.util.PriorityQueue.toArray(arr[]) method.




    // Java code to illustrate toArray(arr[])
    import java.util.*;
      
    public class PriorityQueueDemo {
        public static void main(String args[])
        {
            // Creating an empty PriorityQueue
            PriorityQueue<String> queue = new PriorityQueue<String>();
      
            // Use add() method to add elements into the Queue
            queue.add("Welcome");
            queue.add("To");
            queue.add("Geeks");
            queue.add("For");
            queue.add("Geeks");
      
            // Displaying the PriorityQueue
            System.out.println("The PriorityQueue: " + queue);
      
            // Creating the array and using toArray()
            String[] arr = new String[5];
            String[] arr1 = queue.toArray(arr);
              
            // Displaying arr
            System.out.println("The arr[] is:");
            for (int j = 0; j < arr.length; j++)
                System.out.println(arr[j]);
              
            // Displaying arr1
            System.out.println();    
            System.out.println("The arr1[] is:");
            for (int i = 0; i < arr1.length; i++)
                System.out.println(arr1[i]);
        }
    }
    Output:
    The PriorityQueue: [For, Geeks, To, Welcome, Geeks]
    The arr[] is:
    For
    Geeks
    To
    Welcome
    Geeks
    
    The arr1[] is:
    For
    Geeks
    To
    Welcome
    Geeks
    

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