Java List与数组之间的转换

最新推荐文章于 2024-02-21 10:34:05 发布

最新推荐文章于 2024-02-21 10:34:05 发布 · 215 阅读

文章标签：

#runtime #java

本文介绍了如何在Java中将数组转换为List以及如何将List转换回数组的具体方法。包括使用Arrays.asList()方法将数组转换为固定大小的List，以及通过List的toArray()方法将List转换为数组的不同实现方式。

1 数组转换为List

调用Arrays类的静态方法asList。

asList

public static <T> List<T> asList(T...a)

Returns a fixed-size list backed by the specified array. (Changes to the returned list "write through" to the array.) This method acts as bridge between array-based and collection-based APIs, in combination with Collection.toArray(). The returned list is serializable and implements RandomAccess.

This method also provides a convenient way to create a fixed-size list initialized to contain several elements:

     List<String> stooges = Arrays.asList("Larry", "Moe", "Curly");

Parameters:

a- the array by which the list will be backed

Returns:

a list view of the specified array

API中提供了一种使用的方法。更为常用的示例代码：

String[] arr = new String[] {"str1", "str2"};
List<String> list = Arrays.asList(arr);

2 List转换为数组

这里的List以ArrayList为例，ArrayList的API提供了两种可供使用的函数。

toArray

public Object[] toArray()

Returns an array containing all of the elements in this list in proper sequence (from first to last element).

The returned array will be "safe" in that no references to it are maintained by this list. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs.

Specified by:

toArrayin interface Collection<E>

Specified by:

toArrayin interface List<E>

Overrides:

toArrayin class AbstractCollection<E>

Returns:

an array containing all of the elements in this list in proper sequence

See Also:

Arrays.asList(Object[])

toArray

public <T> T[] toArray(T[]a)

Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array. If the list fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this list.

If the list fits in the specified array with room to spare (i.e., the array has more elements than the list), the element in the array immediately following the end of the collection is set tonull. (This is useful in determining the length of the listonlyif the caller knows that the list does not contain any null elements.)

Specified by:

toArrayin interface Collection<E>

Specified by:

toArrayin interface List<E>

Overrides:

toArrayin class AbstractCollection<E>

Parameters:

a- the array into which the elements of the list are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.

Returns:

an array containing the elements of the list

Throws:

ArrayStoreException- if the runtime type of the specified array is not a supertype of the runtime type of every element in this list

NullPointerException- if the specified array is null

示例代码：

List<String> list = new ArrayList<String>();
list.add("str1");
list.add("str2");
int size = list.size();
String[] arr = (String[])list.toArray(new String[size]);//使用了第二种接口，返回值和参数均为结果