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PriorityQueue toArray() Method in Java

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

   // 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

   // 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

   // 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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