Max Heap - percolateDown Method

Question

I have the workings of a percolateDown method but it doesn't totally work because the operator < is undefined for the argument type(s) E and E. I was wondering if I could get some advice on how to compare the three statements I have that are using "<" and ">".

Thanks!

private E[] arr; //instance variable
private int size; //instance variable


private void percolateDown(int index) {
    if (index >= (size / 2) && index <= size)
            return;
        
    if (arr[index] < arr[leftChildIndex(index)] ||
        arr[index] < arr[rightChildIndex(index)]) {
            
            if (arr[leftChildIndex(index)] > arr[rightChildIndex(index)]) {
                            swap(index, leftChildIndex(index));
                            percolateDown(leftChildIndex(index));
                
                        } else {
                            swap(index, rightChildIndex(index));
                            percolateDown(rightChildIndex(index));
                        }
    }
}