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:
   import java.util.*;
public class PriorityQueueDemo {
`public` `static` `void` `main(String args[]) ` {
`PriorityQueue<String> queue = ` `new` `PriorityQueue<String>(); ` queue.add( "Welcome" );
`queue.add(` `"To"` `); ` queue.add( "Geeks" );
`queue.add(` `"For"` `); ` queue.add( "Geeks" );
`System.out.println(` `"The PriorityQueue: "` `+ queue); ` 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:
   import java.util.*;
public class PriorityQueueDemo {
`public` `static` `void` `main(String args[]) ` {
`PriorityQueue<Integer> queue = ` `new` `PriorityQueue<Integer>(); ` queue.add( 10 );
`queue.add(` `15` `); ` queue.add( 30 );
`queue.add(` `20` `); ` queue.add( 5 );
`queue.add(` `25` `); ` System.out.println( "The PriorityQueue: " + queue);
`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.
     import java.util.*;
public class PriorityQueueDemo {
`public` `static` `void` `main(String args[]) ` {
`PriorityQueue<String> queue = ` `new` `PriorityQueue<String>(); ` queue.add( "Welcome" );
`queue.add(` `"To"` `); ` queue.add( "Geeks" );
`queue.add(` `"For"` `); ` queue.add( "Geeks" );
`System.out.println(` `"The PriorityQueue: "` `+ queue); ` String[] arr = new String[ 5 ];
`String[] arr1 = queue.toArray(arr); ` System.out.println( "The arr[] is:" );
`for` `(` `int` `j = ` `0` `; j < arr.length; j++) ` System.out.println(arr[j]);
`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