Java Convert Unknown Primitive Array to Object Array

Question

I have been trying to create my own library to serialize and de-serialize primitive types from a class to xml and from xml to a class instance using reflection to examine method naming patterns and method return types.

So far I have been able to do this with all the basic primitive types but I got stuck on serializing an array of the same primitives.

For example I invoke the class method to get the array of primitives:

method.invoke(clazz, (Object[])null);

This method will return only a primitive array int[], double[], float[], char[] etc. though we don't know which one it will be.

I have tried using a generic such as

T t = (T)method.invoke(clazz, (Object[])null);
T[] t = (T[])method.invoke(clazz, (Object[])null);

But it doesn't let me cast from the primitive array to an object.

And you can't use Array.newInstance assuming we don't know the type.

Is there a way that I can convert this array of primitives to say an Object array in a generic manner.

In a generic manner meaning without needing to know or checking what the type of the array is. Or should I just cycle through all the primitive types and handle all of them separately.

I can do this both ways the only reason I want to do this in a generic manner is to cut down on the redundant code.

Thanks in advance.

Peter Lawrey · Accepted Answer · 2013-05-31 21:30:16Z

15

You can use the Array utility class

public static Object[] toObjectArray(Object array) {
    int length = Array.getLength(array);
    Object[] ret = new Object[length];
    for(int i = 0; i < length; i++)
        ret[i] = Array.get(array, i);
    return ret;
}

answered May 31, 2013 at 21:30

Peter Lawrey

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1 Comment

Andrew Cumming Over a year ago

It worked perfectly. I never thought that I could access the object as an array. Thank you.

andrew cooke · Accepted Answer · 2013-05-31 21:30:41Z

0

Does java.lang.reflect.Array.get() do what you want?

answered May 31, 2013 at 21:30

andrew cooke

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2 Comments

Peter Lawrey Over a year ago

You also need the getLength()

Andrew Cumming Over a year ago

It would be my next step. This would allow me to get an item from the array but I still need to know how to store it in a proper array first.

Joop Eggen · Accepted Answer · 2013-05-31 21:43:40Z

0

Object result = method.invoke(clazz, (Object[])null);
Class<?> arrayKlazz = result.getClass();
if (arrayKlazz.isArray()) {
    Class<?> klazz = result.getComponentType();
    if (klazz == int.class) {
        int[] intArray = arrayKlazz.cast(result);
    }
}

It seems more appropiate to hold (primitive) arrays in an Object (result above).

edited May 31, 2013 at 21:43

answered May 31, 2013 at 21:32

Joop Eggen

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2 Comments

Peter Lawrey Over a year ago

How will this help get an Object[] from the result?

Joop Eggen Over a year ago

Object[] is already answered. But solving the problem of serialization with Object[] for an int[], double[] etcetera seems a bit going too far. A general array should be held in an Object. I want to suggest that without too large emphasis. If an Object[] is wished - fine.

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