CODEWITHSUNDEEP
javaarraysgenericsclasscastexception
Curious
Curious

Reputation: 921

java generic array and Classcast exception

I had declared BinaryTree as below :

public class BinaryTree<T extends Comparable<T>> {}

But when I call 

Character[] actual = binaryTreeChar.preOrderTraversal(root, Character[].class);

it is throwing exception as below.

java.lang.ClassCastException: [[Ljava.lang.Character; cannot be cast to [Ljava.lang.Comparable;

Is there any better way to deal these cases ?

public T[] preOrderTraversal(BinaryNode<T> root, Class<T[]> clazz) {
        if (root == null)
            return null;
        T[] array = (T[]) Array.newInstance(clazz, count);
        Stack<BinaryNode<T>> stack = new Stack<>();
        stack.push(root);
        int i = 0;
        while (!stack.empty()) {
            BinaryNode<T> next = stack.pop();
            array[i++] = next.data;
            if (next.right != null)
                stack.push(next.right);
            if (next.left != null)
                stack.push(next.left);
        }
        return array;
    }


}

Upvotes: 2

Views: 63

Answers (1)

Eran
Eran

Reputation: 393771

It should be:

public T[] preOrderTraversal(BinaryNode<T> root, Class<T> clazz)

And:

Character[] actual = binaryTreeChar.preOrderTraversal(root, Character.class);

As it is now, you are creating an instance of a Character[][] (i.e. a two dimensional array).

The Class passed to Array.newInstance is the component type of the array, not the array type.

Object java.lang.reflect.Array.newInstance(Class componentType, int length) throws NegativeArraySizeException

Creates a new array with the specified component type and length...

Parameters:

componentType the Class object representing the component type of the new array
length the length of the new array

Upvotes: 2

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