Error when compiling Derivative method for Polynomial Class

Question

Hi guys, doing my homework and I am getting this error for my piece of code.
Error: Operator * cannot be applied to DataElement,int
this is my method
public Polynomial derivative(Polynomial q)
        int size = q.length;
        int i;
        double der[]= new double[size];
        DoubleElement p = new DoubleElement();
        Polynomial temp = new Polynomial(size);
        for(i = 0; i < q.length; i++)
            p.makeCopy((DoubleElement) list);
temp.list[i] = list[i].getCopy() * i;
return temp;
Not sure if it is a stupid error or what not, let me know if you need the class as well. Thanks in advance.

Answer 1

My DoubleElement looks like this
public class DoubleElement extends DataElement
    protected double num;
    public DoubleElement()
        num = 0.0;
    public DoubleElement(double x)
        num = x;
    public DoubleElement(DoubleElement other)
        num = other.num;
    public boolean equals(DataElement otherElement)
        DoubleElement temp = (DoubleElement) otherElement;
        return (num == temp.num);
    public int compareTo(DataElement otherElement)
        DoubleElement temp = (DoubleElement) otherElement;
        if(num < temp.num)
          return -1;
        else
           if(num > temp.num)
              return 1;
           else
              return 0;
        public void setNum(double x)
        num = x;
    public double getNum()
        return num;
    public void makeCopy(DataElement otherElement)
          DoubleElement temp = (DoubleElement) otherElement;
          num = temp.num;
    public DataElement getCopy()
        DoubleElement temp = new DoubleElement(num);
        return temp;
    public String toString()
        return String.valueOf(num);
}