Converting an array of objects to an array of their primitive types

Question

If you have an array of Java objects which have a primitive type (for example Byte, Integer, Char, etc). Is there a neat way I can convert it into an array of the primitive type? In particular can this be done without having to create a new array and loop through the contents.

So for example, given

Integer[] array 

what is the neatest way to convert this into

int[] intArray 

Unfortunately, this is something we have to do quite frequently when interfacing between Hibernate and some third party libraries over which we have no control. It seems this would be a quite common operation so I would be surprised if there's no shortcut.

Thanks for your help!

Answer 1

Once again, Apache Commons Lang is your friend. They provide ArrayUtils.toPrimitive() which does exactly what you need. You can specify how you want to handle nulls.

Answer 2

With streams introduced in Java 8 this can be done:

int[] intArray = Arrays.stream(array).mapToInt(Integer::intValue).toArray(); 

However, there are currently only primitive streams for int, long and double. If you need to convert to another primitive type such as byte the shortest way without an external library is this:

byte[] byteArray = new byte[array.length]; for(int i = 0; i < array.length; i++) byteArray[i] = array[i]; 

Or the for loop can be replaced with a stream if you want:

IntStream.range(0, array.length).forEach(i -> byteArray[i] = array[i]); 

All of these will throw a NullPointerException if any of your elements are null.