java - 将对象数组转换回整数数组时出现问题

Question

当我运行这个时，我收到错误:

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.Integer; at Main.main(Main.java:30)

public class Main 
{ 
    private interface Function<R, D> 
    { 
        public R apply(D parameter);
    }

    public static void main(String[] args) 
    {           
        // Example 1
        Function<Integer, Integer> function = new CalculateSuccessor();
        Integer[] integerArray = {1, 3, 4, 2, 5};
        PrintArray(map(function, integerArray)); // map returns {2, 4, 5, 3, 6}  <--- line 30
    }

    @SuppressWarnings({"unchecked"})
    public static <R, D> R[] map(Function<R, D> function, D[] array)
    {
        R[] results = (R[]) new Object[array.length];

        // Iterate through the source array, apply the given function, and record results
        for (int i = 0; i < array.length; i++)
        {
            results[i] = (R)function.apply(array[i]);
        }

        return results;  
    }

    public static <T> void PrintArray(T[] array)
    {
        for (T element : array)
        {
            System.out.println(element.toString());
        }   
    } 
}

Answer 1

问题是结果数组被创建为 new Object[array.length]。强制转换 (R[]) 不会将此数组转换为其他类型，它只是告诉编译器将其视为 R[]。请参阅Quick Java question: Casting an array of Objects into an array of my intended class 。创建泛型类型的数组有点令人讨厌 - 您可以通过谷歌搜索各种解决方案，例如How to create a generic array in Java? - 但通常最简单的方法是使用列表而不是数组:您可以使用 new ArrayList

创建它