ArrayList.toArray() 未转换为正确的类型？

Question

所以，我得到的是：

class BlahBlah
{
    public BlahBlah()
    {
        things = new ArrayList<Thing>();
    }

    public Thing[] getThings()
    {
        return (Thing[]) things.toArray();
    }

    private ArrayList<Thing> things;
}

在另一个类中我得到：

for (Thing thing : someInstanceOfBlahBlah.getThings())
{
    // some irrelevant code
}

错误是：

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [LsomePackage.Thing;
at somePackage.Blahblah.getThings(Blahblah.java:10)

我怎样才能解决这个问题？

Answer 1

尝试：

public Thing[] getThings()
{
    return things.toArray(new Thing[things.size()]);
}

您的原始版本不起作用的原因是 toArray() 返回 Object[] 而不是 Thing[]。您需要使用另一种形式的 toArray -- toArray(T[]) -- 获取 Things 数组。

Answer 2

尝试

private static final Thing[] NO_THING = {};

并

return (Thing[]) things.toArray(NO_THING);

Answer 3

有 2 个 toArray() 函数。

    Object[] toArray()
        Returns an array containing all of the elements in this list in the correct order.
    <T> T[] toArray(T[] a)
        Returns an array containing all of the elements in this list in the correct order;
        the runtime type of the returned array is that of the specified array.

您正在使用第一个，它应该返回 Object[] 并且它正在这样做。如果您想获得正确的类型，请使用第二个版本：

things.toArray(new Thing[things.length]);

或者如果您不想在 new Thing[things.length] 上浪费更多空间，则只需将循环更改为强制转换：

Thing thing = null;
for (Object o : someInstanceOfBlahBlah.getThings())
{
    thing = (Thing) o;
    // some unrelevant code
}

Answer 4

尝试

things.toArray(new Thing[0])

列表。 toArray javadoc