Convert list to array in Java [duplicate]

How can I convert a List to an Array in Java?

Check the code below:

ArrayList<Tienda> tiendas;
List<Tienda> tiendasList; 
tiendas = new ArrayList<Tienda>();

Resources res = this.getBaseContext().getResources();
XMLParser saxparser =  new XMLParser(marca,res);

tiendasList = saxparser.parse(marca,res);
tiendas = tiendasList.toArray();

this.adaptador = new adaptadorMarca(this, R.layout.filamarca, tiendas);
setListAdapter(this.adaptador);  

I need to populate the array tiendas with the values of tiendasList.

Solution 1:

Either:

Foo[] array = list.toArray(new Foo[0]);

or:

Foo[] array = new Foo[list.size()];
list.toArray(array); // fill the array

Note that this works only for arrays of reference types. For arrays of primitive types, use the traditional way:

List<Integer> list = ...;
int[] array = new int[list.size()];
for(int i = 0; i < list.size(); i++) array[i] = list.get(i);

Update:

It is recommended now to use list.toArray(new Foo[0]);, not list.toArray(new Foo[list.size()]);.

From JetBrains Intellij Idea inspection:

There are two styles to convert a collection to an array: either using a pre-sized array (like c.toArray(new String[c.size()])) or using an empty array (like c.toArray(new String[0]).

In older Java versions using pre-sized array was recommended, as the reflection call which is necessary to create an array of proper size was quite slow. However since late updates of OpenJDK 6 this call was intrinsified, making the performance of the empty array version the same and sometimes even better, compared to the pre-sized version. Also passing pre-sized array is dangerous for a concurrent or synchronized collection as a data race is possible between the size and toArray call which may result in extra nulls at the end of the array, if the collection was concurrently shrunk during the operation.

This inspection allows to follow the uniform style: either using an empty array (which is recommended in modern Java) or using a pre-sized array (which might be faster in older Java versions or non-HotSpot based JVMs).

Solution 2:

An alternative in Java 8:

String[] strings = list.stream().toArray(String[]::new);

Since Java 11:

String[] strings = list.toArray(String[]::new);

Solution 3:

I think this is the simplest way:

Foo[] array = list.toArray(new Foo[0]);

Solution 4:

I came across this code snippet that solves it.

//Creating a sample ArrayList 
List<Long> list = new ArrayList<Long>();

//Adding some long type values
list.add(100l);
list.add(200l);
list.add(300l);

//Converting the ArrayList to a Long
Long[] array = (Long[]) list.toArray(new Long[list.size()]);

//Printing the results
System.out.println(array[0] + " " + array[1] + " " + array[2]);

The conversion works as follows:

1. It creates a new Long array, with the size of the original list
2. It converts the original ArrayList to an array using the newly created one
3. It casts that array into a Long array (Long[]), which I appropriately named 'array'