[英]ClassCastException when casting object Array to Long array
I get this exception when i try to cast an Object array to a Long array. 当我尝试将Object数组转换为Long数组时,我得到此异常。
Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object;
线程“main”中的异常java.lang.ClassCastException:[Ljava.lang.Object; cannot be cast to [Ljava.lang.Long;
不能投[Ljava.lang.Long;
My keys in my hotelRooms map are Long, why it is not possible to cast. 我在hotelRooms地图中的钥匙很长,为什么不能施展。 Does someone know how to solve this.
有人知道如何解决这个问题。
public class ObjectArrayToLongArrayTest {
private Map<Long, String[]> hotelRooms;
public static void main(String[] args) {
ObjectArrayToLongArrayTest objectArrayToLongArrayTest =
new ObjectArrayToLongArrayTest();
objectArrayToLongArrayTest.start();
objectArrayToLongArrayTest.findByCriteria(null);
}
private void start() {
hotelRooms = new HashMap<Long, String[]>();
// TODO insert here some test data.
hotelRooms.put(new Long(1), new String[] {
"best resort", "rotterdam", "2", "y", "129", "12-12-2008",
"11111111"
});
hotelRooms.put(new Long(2), new String[] {
"hilton", "amsterdam", "4", "n", "350", "12-12-2009", "2222222"
});
hotelRooms.put(new Long(3), new String[] {
"golden tulip", "amsterdam", "2", "n", "120", "12-09-2009",
null
});
}
public long[] findByCriteria(String[] criteria) {
Long[] returnValues;
System.out.println("key of the hotelRoom Map" + hotelRooms.keySet());
if (criteria == null) {
returnValues = (Long[]) hotelRooms.keySet().toArray();
}
return null;
}
}
change 更改
returnValues = (Long[]) hotelRooms.keySet().toArray();
to 至
returnValues = hotelRooms.keySet().toArray(new Long[hotelRooms.size()]);
and let me know if it works :-) 让我知道它是否有效:-)
It's because Object[] Set.toArray()
returns an object array. 这是因为
Object[] Set.toArray()
返回一个对象数组。 You can't downcast the array to a more specific type. 您无法将数组转发为更具体的类型。 Use
<T> T[]Set.toArray(T[] a)
instead. 请改用
<T> T[]Set.toArray(T[] a)
。 If the generic type method didn't exist you'd have to loop through each of the Objects in the return object array and cast each individually into a new Long array. 如果泛型类型方法不存在,则必须循环遍历返回对象数组中的每个对象,并将每个对象单独转换为新的Long数组。
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