casting a generic array in java

Question

The implementation is for a linked list in java :

public AnyType[] toArr() {

        AnyType[] arr = (AnyType[]) new Object[size];

        int i = 0;
        Node<AnyType> current = head.next;
        while (cur != head){

            arr[i] = current.data;// fill the array
            i++;
            current = current.next;

        }      

    return arr;

}

public static void main(String[] args) {
    System.out.println(ll.toArr().toString());
}

The error that I get:

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

Thanks.

Mike Samuel · Accepted Answer · 2011-02-27 15:36:33Z

4

An Object[] is not a sub-type of AnyType[] so the cast is illegal.

To create an array of a particular type, you can use the reflective java.lang.reflect.Array.newInstance factory method : http://download.oracle.com/javase/1.5.0/docs/api/java/lang/reflect/Array.html#newInstance(java.lang.Class,%20int)

So if you had a Class instance for the AnyType type:

Class<? extends AnyType> anyTypeClass = ...;
AnyType[] newArray = (AnyType[]) Array.newInstance(anyTypeClass, length);

If you want to deal with primitive types, you can do that with java.lang.reflect.Array.

Object myPrimitiveArray = Array.newInstance(Integer.TYPE, length);

but since you can't cast it to an Object[] you need to use reflection to modify it as well:

Array.set(myPrimitiveArray, 0, myPrimitiveWrapperObject);

answered Feb 27, 2011 at 15:36

Mike Samuel

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