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
.
The best and easiest way to convert a List into an Array in Java is to use the . toArray() method. Likewise, we can convert back a List to Array using the Arrays. asList() method.
Java allows you to copy arrays using either direct copy method provided by java. util or System class. It also provides a clone method that is used to clone an entire array.
Using a Copy Constructor: Using the ArrayList constructor in Java, a new list can be initialized with the elements from another collection. Syntax: ArrayList cloned = new ArrayList(collection c); where c is the collection containing elements to be added to this list.
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);
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).
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