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;
}

在另一堂课中我得到了：

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)

我该如何解决这个问题？

Answer 1

尝试：

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

原始版本不起作用的原因是toArray()返回Object[]而不是Thing[]。您需要使用其他形式的toArray - toArray(T[]) - 来获取Things数组。

Answer 2

尝试

private static final Thing[] NO_THING = {};

和

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

Answer 3

有2 toArray() functions。

    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.

你正在使用第一个，它应该返回Object[]并且它正在这样做。如果要获得正确的类型，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，那么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

试

things.toArray(new Thing[0])

List.toArray javadoc

ArrayList.toArray（）没有转换为正确的类型？

4 个答案: