PriorityQueue toArray() Method in Java

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