ArrayList.toArray（）不轉換爲正確的類型？

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; 
} 

在其他類我：

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

和錯誤是：

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

我怎樣才能解決這個問題？

Answer 1

嘗試：

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

的原因，你的原始版本不工作是toArray()回報Object[]而不是Thing[]。您需要使用其他形式的toArray - toArray(T[]) - 才能獲得Things的數組。

Answer 2

嘗試

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. 

您使用的是第一位的，這是應該返回Object[]和它這樣做。如果你想獲得正確的類型使用第二個版本：

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

，或者如果你不想浪費任何new Thing[things.length]更多的空間，那麼就改變回路投：

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

Answer 4

嘗試

things.toArray(new Thing[0]) 

List.toArray javadoc