Java 数组内置函数toArray详解

java.util.List中的toArray函数

java.util.List<E> @NotNull

public abstract <T> T[] toArray(@NotNull 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 list 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.)

Like the toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this

method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.

Suppose x is a list known to contain only strings. The following code can be used to dump the list into a newly allocated array of String:

String[] y = x.toArray(new String[0]);

Note that toArray(new Object[0]) is identical in function to toArray().

Overrides:

toArray in interface Collection

Params:

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

Type parameters:

<T> – the runtime type of the array to contain the collection

Returns:

an array containing the elements of this 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

External annotations:

Abstract method toArray: @org.jetbrains.annotations.NotNull

Parameter a: @org.jetbrains.annotations.NotNull

翻译
java.util.List @NotNull

public abstract T[] toArray(@NotNull T[] a)