java - 在Java中将列表转换为数组

Question

如何在 Java 中将 List 转换为 Array？

检查下面的代码:

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);  

我需要用 tiendasList 的值填充数组 tiendas。

Answer 1

要么:

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

或:

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

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请注意，这仅适用于引用类型的数组。对于原始类型的数组，使用传统方式:

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

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更新:

现在推荐使用list.toArray(new Foo[0]);，而不是list.toArray(new Foo[list.size()]);.

来自 JetBrains Intellij Idea 检查:

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).