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PriorityQueue toArray() Method in Java

Last Updated : 10 Dec, 2018
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  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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