Check if variable contains an array

Question

I am trying to create a method in Java that reverses an array or matrix. The method's code as it is now looks like this:

@SuppressWarnings("unchecked")
public static <T> T[] reverse(T[] array) {
    T[] ret = Array.newInstance(array.getClass().getComponentType(), array.length);
    for(int i = 0; i < array.length; i++) {
        if (array[i].getClass().getComponentType() != null) {
            ret[array.length - 1 - i] = (T) reverse((T[]) array[i]); // the exception (see below) occurs here
        } else {
            ret[array.length - 1 - i] = array[i];
        }
    }
    return ret;
}

When I tried to run this method with a 2-dimensional String matrix, it worked out well. Now I tried to use an 2-dimensional int matrix instead and I get the following exception:

Exception in thread "main" java.lang.ClassCastException: [I cannot be cast to [Ljava.lang.Object;

~~How come this code works with String arrays, but not with int arrays? How can I fix the code to work with int arrays as well?~~

@EDIT I just noticed that I asked this question wrong. *facepalms* What I originally wanted to know is: how do I check if array[i] is an array or not?

because int is not an Object

mprabhat
– mprabhat

2014-11-27 09:45:02 +00:00
Commented Nov 27, 2014 at 9:45 — mprabhat
– mprabhat, Commented Nov 27, 2014 at 9:45

Maroun · Accepted Answer · 2014-11-27 09:45:47Z

4

Use Integer instead. int is a primitive type where String is an object type.

See Restrictions on Generics:

Cannot Instantiate Generic Types with Primitive Types

See also the example they provide:

Quote >

class Pair<K, V> {

    private K key;
    private V value;

    public Pair(K key, V value) {
        this.key = key;
        this.value = value;
    }

    // ...
}

When creating a Pair object, you cannot substitute a primitive type for the type parameter K or V:

Pair<int, char> p = new Pair<>(8, 'a');  // compile-time error

<

answered Nov 27, 2014 at 9:45

Maroun

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2 Comments

mezzodrinker Over a year ago

I'm sorry, I asked this question wrong. Your answer is - of course - correct concerning my problems with String[] and int[], but I originally wanted to know how I can check if a variable is an array or not.

Maroun Over a year ago

@flashdrive2049 if(someObj.getClass().isArray())? Or if(someObj instanceof Object[])

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