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
你可以像下面这样使用toArray() api:
ArrayList<String> stringList = new ArrayList<String>();
stringList.add("ListItem1");
stringList.add("ListItem2");
String[] stringArray = new String[stringList.size()];
stringArray = stringList.toArray(stringList);
数组中的值为:
for(String value : stringList)
{
System.out.println(value);
}
其他回答
我遇到了这个代码片段来解决这个问题。
//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]);
转换过程如下:
它创建了一个新的Long数组，其大小与原始列表相同 它将原始的ArrayList转换为使用新创建的数组 它将该数组转换为长数组(Long[])，我将其适当地命名为'array'
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);
在没有Java 8的情况下，我想到的最好的事情是:
public static <T> T[] toArray(List<T> list, Class<T> objectClass) {
if (list == null) {
return null;
}
T[] listAsArray = (T[]) Array.newInstance(objectClass, list.size());
list.toArray(listAsArray);
return listAsArray;
}
如果有人有更好的方法，请分享:)
以下(Ondrej的回答):
Foo[] array = list.toArray(new Foo[0]);
Is the most common idiom I see. Those who are suggesting that you use the actual list size instead of "0" are misunderstanding what's happening here. The toArray call does not care about the size or contents of the given array - it only needs its type. It would have been better if it took an actual Type in which case "Foo.class" would have been a lot clearer. Yes, this idiom generates a dummy object, but including the list size just means that you generate a larger dummy object. Again, the object is not used in any way; it's only the type that's needed.
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]);
}
