Java PriorityQueue toArray() Method

The toArray() method of PriorityQueue class returns an array containing all the elements present in the queue where the elements are present in no particular order.

The array is returned, if the queue fits in the specified array. Else, a new array is allocated with the same type of the array and size of the queue.

Syntax

public Object[] toArray()
public <T> T[] toArray(T[] a)

Parameter

a - this is the array in which the elements of the queue will be stored.

Type Parameters

T - this is the runtime type of the array to hold the collection.

Specified By

The toArray() method of PriorityQueue class is specified by toArray() method in interface Collection<E>.

Override

The toArray() method of PriorityQueue class isoverrided by toArray() method in class AbstractCollection<E>.

Return Value

The toArray() method returns an array that contains all the elements of this queue.

Example 1

import java.util.PriorityQueue;

public class PriorityQueueToArrayExample1 {
public static void main(String[] args) {
PriorityQueue<String>Pqueue = new PriorityQueue<String>();
Pqueue.add("Reema");
Pqueue.add("Rahul");
Pqueue.add("Rita");
Pqueue.add("Ramesh");
        Object[] a=Pqueue.toArray();
for(int i=0 ;i<a.length;i++){
System.out.println("Element : "+a[i]);
        }
    }
}

Test it Now

Output:

Element : Rahul
Element : Ramesh
Element : Rita
Element :Reema

Example 2

import java.util.PriorityQueue;

public class PriorityQueueToArrayExample2 {
public static void main(String[] args) {
PriorityQueue<Integer>Pqueue = new PriorityQueue<Integer>();
Pqueue.add(8);
Pqueue.add(5);
Pqueue.add(17);
Pqueue.add(80);
Pqueue.add(2);
System.out.println(Pqueue);
        Object[] a = Pqueue.toArray();
for (int i = 0; i <a.length; i++) {
System.out.print(a[i] + " ");
        }
System.out.println("Ascending order : ");
for (int i = 0; i <a.length; i++) {
for (int j = i + 1; j <a.length; j++) {
                Object temp = 0;
if (a[i] > a[j]) {
                    temp = a[i];
                    a[i] = a[j];
                    a[j] = temp;
                }
            }
        }
for (int i = 0; i <a.length; i++) {
System.out.print(a[i] + " ");
        }

    }
}

Test it Now

Output:

Error:(20, 24) java: bad operand types for binary operator '>'
first type:  java.lang.Object
second type: java.lang.Object

Note: Operator ?>? cannot be applied to ?java.lang.object?.

Example 3 is the solution of the above described problem.

Example 3

import java.util.PriorityQueue;

public class PriorityQueueToArrayExample3 {
public static void main(String[] args) {

PriorityQueue<Integer>Pqueue = new PriorityQueue<Integer>();
Pqueue.add(8);
Pqueue.add(5);
Pqueue.add(17);
Pqueue.add(80);
Pqueue.add(2);

        Integer[] a = new Integer[5];
        Integer[] b = Pqueue.toArray(a);
System.out.print("Elements : ");
for (int i = 0; i <a.length; i++) {
System.out.print(a[i]+" ");
        }
System.out.println();
System.out.print("Ascending order : ");
for (int i = 0; i <b.length; i++) {
for (int j = i + 1; j <b.length; j++) {
int temp = 0;
if (a[i] > a[j]) {
                    temp = b[i];
                    b[i] = b[j];
                    b[j] = temp;
                }
            }
        }
for (int i = 0; i <b.length; i++) {
System.out.print(b[i] + " ");
        }
    }
}

Test it Now

Output:

Elements : 2 5 17 80 8 
Ascending order : 2 5 8 17 80

Example 4

import java.util.PriorityQueue;

public class PriorityQueueToArrayExample4 {
public static void main(String[] args) {
PriorityQueue<String>Pqueue = new PriorityQueue<String>();
Pqueue.add("Reema");
Pqueue.add("Rahul");
Pqueue.add("Rita");
Pqueue.add("Ramesh");
        Object[] a=Pqueue.toArray(null);
for(int i=0 ;i<a.length;i++){
System.out.println("Element : "+a[i]);
        }
    }
}

Test it Now

Output:

Exception in thread "main" java.lang.NullPointerException
	atjava.util.PriorityQueue.toArray(PriorityQueue.java:469)
	at com.javaTpoint.PriorityQueueToArrayExample5.main(PriorityQueueToArrayExample4.java:12)

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