将对象Array转换为Long数组时出现ClassCastException

Question

当我尝试将Object数组转换为Long数组时,我得到此异常.

线程"main"中的异常java.lang.ClassCastException:[Ljava.lang.Object; 不能投[Ljava.lang.Long;

我在hotelRooms地图中的钥匙很长,为什么不能施展.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;
}
}   

Answer 1

更改

returnValues = (Long[]) hotelRooms.keySet().toArray();

至

returnValues = hotelRooms.keySet().toArray(new Long[hotelRooms.size()]);

让我知道它是否有效:-)

Answer 2

这是因为Object[] Set.toArray()返回一个对象数组.您无法将数组转发为更具体的类型.请<T> T[]Set.toArray(T[] a)改用.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.