Question

I understand that for every primitive type in java there is a reference type that can represent the same values, plus null. For example, int and java.lang.Integer.

I also understand that while all arrays (even java.lang.Object[]) derive from java.lang.Object, only arrays of non-primitive types can be converted to java.lang.Object[].

In other words, we can do:

Class type = Integer.class;
Object[] o = (Object[])java.lang.reflect.Array.newInstance(type, 4);

but the following results in an exception:

Class type = int.class;
Object[] o = (Object[])java.lang.reflect.Array.newInstance(type, 4);

so in that particular case we could do:

 Class type = int.class;
 Object o = java.lang.reflect.Array.newInstance(type, 4);

…which seems fine, until one wonders how to add elements to an Object that represents an array that cannot be converted to Object[].

is the only way around this problem to check the type of the elements of the array and cast the Object as appropriate?

ie:

  if (type == int.class)
  ((int[])o)[0] = getFirstElement();

  else if (type == short.class)
  ((short[])o[0] = getFirstElement();

Answer 1

Besides creating arrays, java.lang.reflect.Array also offers methods to get and set elements in arrays:

Class<?> type = int.class;
Object array = java.lang.reflect.Array.newInstance(type, 4);

int index = 0;
Object value = getFirstElement();
java.lang.reflect.Array.set(array, index, value);

Also note from the documentation that the value is first automatically unwrapped if the array has a primitive component type. So this should work for any array, including those that do not inherit from Object[].

There is a corresponding Object get(Object array, int index) method too.