PriorityQueue toArray(IntFunction) in Java

toArray(IntFunction<K[]>): This method is available in java.util.PriorityQueue class of Java.

Syntax:

<K> K[] java.util.Collection.toArray(IntFunction<K[]> generator)

This method takes one argument. This method returns an array containing all of the elements in this collection, using the provided generator function to allocate the returned array.

Parameters: One parameter is required for this method.

generator: a function which produces a new array of the desired type and the provided length.

Returns: an array containing all of the elements in this collection.

Throws:

1. ArrayStoreException - if the runtime type of any element in this collection is not assignable to the runtime component type of the generated array.

2. NullPointerException - if the generator function is null.

Approach 1: When no exception

Java

import java.util.Arrays;
import java.util.PriorityQueue;
import java.util.function.IntFunction;

public class PriorityQueuetoArray2 {
    public static void main(String[] args) {

        PriorityQueue<Integer> priorityQueue = 
                      new PriorityQueue<Integer>();

        priorityQueue.add(12);
        priorityQueue.add(5);
        priorityQueue.add(10);
        priorityQueue.add(2);

        IntFunction<Integer[]> intFunction = 
               new IntFunction<Integer[]>() {

            @Override
            public Integer[] apply(int value) {
                Integer[] string = { 1, 2 };
                return string;

            }
        };

        System.out.println(Arrays.
                toString(priorityQueue.toArray(intFunction)));

    }
}

Output:

[2, 5, 10, 12]

Approach 2: NullPointerException 

Java

import java.util.Arrays;
import java.util.PriorityQueue;
import java.util.function.IntFunction;

public class PriorityQueuetoArray2 {
    public static void main(String[] args) {

        PriorityQueue<Integer> priorityQueue = 
                      new PriorityQueue<Integer>();

        priorityQueue.add(12);
        priorityQueue.add(5);
        priorityQueue.add(10);
        priorityQueue.add(2);

        IntFunction<Integer[]> intFunction = null;

        System.out.println(Arrays.
                toString(priorityQueue.toArray(intFunction)));

    }
}

Output:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.util.function.IntFunction.apply(int)" because "generator" is null
	at java.base/java.util.Collection.toArray(Collection.java:413)