java list與數組之間的轉換詳細解析
1 數組轉換為List
調用Arrays類的靜態(tài)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
用法：API中提供了一種使用的方法。更為常用的示例代碼：
String[] arr = new String[] {"str1", "str2"};
List<String> list = Arrays.asList(arr);
2 List轉換為數組
這里的List以ArrayList為例，ArrayList的API提供了兩種可供使用的函數。
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:
toArray in interface Collection<E>
Specified by:
toArray in interface List<E>
Overrides:
toArray in 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 to null. (This is useful in determining the length of the list only if the caller knows that the list does not contain any null elements.)
Specified by:
toArray in interface Collection<E>
Specified by:
toArray in interface List<E>
Overrides:
toArray in 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
用法：示例代碼：
List<String> list = new ArrayList<String>();
list.add("str1");
list.add("str2");
int size = list.size();
String[] arr = (String[])list.toArray(new String[size]);//使用了第二種接口，返回值和參數均為結果
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