如何将 java Object 转换为 Object[]？

Question

How to cast java Object to java Object[] or Integer[] Error(I cannot be cast to [Ljava.lang.Object;);

public class LongestAscendingSumSequence {

    public static void main(String[] ar) {
        int[] arr = { 1, 2, 3, 20, 3, 25, 30, 31, 32, 33, 34 };
        System.out.println(getSum(arr));
        float[] brr = { 1.3f, 2.3f };
        System.out.println(getSum(brr));
        int[] crr = { 1, 2, 3, 20, 3, 25, 30, 31, 32, 33, 34, -2 };
        System.out.println(getSum(crr));

    }

    public static String getSum(Object obj) {
        Object[] objects = (Object[]) obj;

        System.out.println(objects.length);

        return null;
    }
}

Getting error for this

Exception in thread "main" java.lang.ClassCastException: [I cannot be cast to [Ljava.lang.Object;
    at jan25.LongestAscendingSumSequence.getSum(LongestAscendingSumSequence.java:16)
    at jan25.LongestAscendingSumSequence.main(LongestAscendingSumSequence.java:7)

Answer 1

You are trying to cast primitive types to Object which is not allowed.

You need Wrapper classes for this approach. Eg:

Integer[] arr = { 1, 2, 3, 20, 3, 25, 30, 31, 32, 33, 34 };
System.out.println(getSum(arr));

Ideone demo

Answer 2

Note: This does not support calculating sum results outside the double range. You should look into BigDecimal if you need that.

public static <T extends Number>double getSum(T[] tArray) {
    double sum = 0;
    for (T t : tArray) sum = sum + t.doubleValue();
    return sum;
}

You need to use Integer[] instead of int[] .

Answer 3

As others pointed out, you should use Wrapper Types here, for example Integer over the primitive int. The classCastException here occurs because it is trying to cast a primitive int to Object type and neither by widening or unchecked narrowing can one reach from int to Object as int doesn't inherit from Object type.