Iterating over arrays by reflection

Question

I am doing some reflection work and go to a little problem.

I am trying to print objects to some GUI tree and have problem detecting arrays in a generic way.

I suggested that :

object instanceof Iterable

Would make the job ,but it does not, (obviously applies only to Lists and Set and whoever implements it.)

So how is that i would recognice an Array Some Object[] , Or long[] or Long[] .. ?

Thanks

score 76 · Accepted Answer · edited Mar 18 '15 at 13:01

76

If you don't want only to check whether the object is an array, but also to iterate it:

if (array.getClass().isArray()) {
    int length = Array.getLength(array);
    for (int i = 0; i < length; i ++) {
        Object arrayElement = Array.get(array, i);
        System.out.println(arrayElement);
    }
}

(the class above is java.lang.reflect.Array)

edited Mar 18 '15 at 13:01

Ralph

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answered Feb 04 '10 at 14:45

Bozho

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score 5 · Answer 2 · edited Sep 28 '10 at 10:32

5

Do you mean Object.getClass().isArray()?

edited Sep 28 '10 at 10:32

Buhake Sindi

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answered Feb 04 '10 at 14:45

Joonas Pulakka

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score 3 · Answer 3 · answered Feb 04 '10 at 14:42

3

You can do

if (o instanceof Object[]) {
  Object[] array = (Object[]) o;
  // now access array.length or 
  // array.getClass().getComponentType()
}

answered Feb 04 '10 at 14:42

Mr. Shiny and New 安宇

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This is good , but it will not apply to the primitive array types. I think i found the answer : object.getClass().isArray() .. lol – Roman Feb 04 '10 at 14:46

score 0 · Answer 4 · answered Sep 14 '11 at 09:43

First of all, @Bozho's answer is perfectly correct.

If you want to make this to be easier useable, I've just created a method in our little OSS utility molindo-utils that turns an array of unknown type into an Iterable: ArrayUtils.toIterable(Object)

This way, you can do:

// any array, e.g. int[], Object[], String[], ...
Object array = ...;
for (Object element : ArrayUtils.toIterable(array)) {
    // element of type Integer for int[]
    System.out.println(element);
}

See README of molindo-utils on how to get molindo-utils or feel free to copy the code if you like, just as you see fit.

Iterating over arrays by reflection

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