PriorityQueue toArray() Method in Java (original) (raw)

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 queue = new PriorityQueue();
     // 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