AbstractCollection toArray() Method in Java

In Java, the toArray() method is the part of the AbstractCollection class. It is used to convert collections like List, Set, etc. into an array. It copies all the elements from the collection into a new array.

Example:

The AbstractCollection: [C, JS, C++, Java]
The array is:
C JS C++ Java 

Now, there are two versions of toArray() method i.e. one without parameter and one with the parameter.

1. toArray() Method

Copies all the elements from the collection into a new array.

Syntax:

Object[] arr = AbstractCollection.toArray();

• Parameter: This method does not take any parameter.
• Return Type: This method returns an array containing the elements of the AbstracrCollection.

Example: This example demonstrates converting a PriorityQueue to an array using the toArray() and printing the array elements.

The AbstractCollection: [5, 10, 25, 20, 15, 30]
The array is:
5 10 25 20 15 30 

2. toArray(arr[]) Method

In Java, toArray(arr[]) method is used to covert an AbstractCollection into an array of specified type. It fills the provided array with the elements of the collection. If the provided array is large enough it is used directly otherwise, a new array of the appropriate type and size is created.

Syntax:

Object[] toArray(T[] arr)

• Parameter: arr[] is the array into which the elements of the collection will be stored.
• Return Type: This method returns an array containing the elements of the collection in the correct order.

Exception:

The toArray(arr[]) method may throws two exceptions:

• ArrayStoreException: If the array type is incompatible with the collection elements.
• NullPointerException: If the provided array is null.

Example 1: This example demonstrates how to convert an AbstractCollection to an array using toArray(arr[]) method when the provided array is of the same size as the collections.

The AbstractCollection: [For, Geeks, Geeks]
The Array is:
For Geeks Geeks 

Example 2: This example demonstrates how the toArray(arr[]) method in java automatically resizes the array when it is smaller than the AbstractCollection size.

The AbstractCollection: [For, Geeks, Geeks, Java]
The Array is:
For Geeks Geeks Java 

Example 3: This example demonstrates how the toArrray(arr[]) method in java copies element from an AbstractCollection to an array, even when the array is larger than the collection.

The AbstractCollection: [For, Geeks, Geeks, Java]
The Array is:
For Geeks Geeks Java null null 

Example 4: This example demonstrates that passing a null array to the toArray() method in Java throw a NullPointerException.