java - 将包含数据的数组传递给 List 的 toArray 方法

Question

我有一些这样的代码:

    String[] colors = {"black", "blue", "yellow", "red", "pink", "green", "cyan"};
    String[] alphabets = {"A", "B", "C", "D", "E", "F", "G", "H", "I"};
    LinkedList<String> links = new LinkedList<>(Arrays.asList(colors));
    System.out.println(links);
    colors = links.toArray(alphabets);
    System.out.println(Arrays.asList(colors));

它的输出是:

[black, blue, yellow, red, pink, green, cyan]
[black, blue, yellow, red, pink, green, cyan, null, I]

第二个输出行中的 null 是什么？为什么？

Answer 1

当您对某个方法的特定行为有疑问时，最好的答案来源是查看文档。

Java 文档指出:

toArray(T[] a)

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.)