如何将列表转换为Java中的数组?
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。
当前回答
Java 8中的替代方案:
String[] strings = list.stream().toArray(String[]::new);
从Java 11开始:
String[] strings = list.toArray(String[]::new);
其他回答
:
Foo[] array = list.toArray(new Foo[0]);
or:
Foo[] array = new Foo[list.size()];
list.toArray(array); // fill the array
注意，这仅适用于引用类型的数组。对于基元类型数组，使用传统方法:
List<Integer> list = ...;
int[] array = new int[list.size()];
for(int i = 0; i < list.size(); i++) array[i] = list.get(i);
更新:
现在建议使用list。toArray(新的Foo[0]);，不是列表。toArray(新Foo [list.size());。
来自JetBrains Intellij Idea的检测:
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).
试试这个:
List list = new ArrayList();
list.add("Apple");
list.add("Banana");
Object[] ol = list.toArray();
对于ArrayList，以下工作:
ArrayList<Foo> list = new ArrayList<Foo>();
//... add values
Foo[] resultArray = new Foo[list.size()];
resultArray = list.toArray(resultArray);
我认为这是最简单的方法:
Foo[] array = list.toArray(new Foo[0]);
这是可行的。种。
public static Object[] toArray(List<?> a) {
Object[] arr = new Object[a.size()];
for (int i = 0; i < a.size(); i++)
arr[i] = a.get(i);
return arr;
}
然后是主要方法。
public static void main(String[] args) {
List<String> list = new ArrayList<String>() {{
add("hello");
add("world");
}};
Object[] arr = toArray(list);
System.out.println(arr[0]);
}
