Question

package polynomial;

/**
 *
 * @author Steven
 */

public class Polynomial
{
private float data;
protected static Polynomial head;
private Polynomial link;

/**
 * @param args the command line arguments
 */    
public Polynomial(float[] data)
{
    head = null;

    if(data.length == 1)
        head = insertAtFront(head, data[0]);

    for(int i = data.length-1; i >= 0; i--)
    {
        System.out.println(head);
        head = insertAtFront(head, data[i]);
    }
}

public Polynomial(float data, Polynomial link)
{
    this.link = link;
    this.data = data;
}

public static Polynomial add(Polynomial p, Polynomial p2)
{
    if(p.length() > p2.length())
    {
        while(p.length() != p2.length())
            {
                insertAtFront(p2, 0);
            }

        for(Polynomial poly = p; poly != null && p2 != null; poly = poly.link)
        {
            p2.data = (p2.data + poly.data);
            p2 = p2.link;
        }
    }
    else if(p2.length() > p.length())
    {
        while(p2.length() != p.length())
            {
                insertAtFront(p, 0);
            }

        for(Polynomial poly = p; poly != null && p2 != null; poly = poly.link)
        {
            p2.data = (p2.data + poly.data);
            p2 = p2.link;
        }
    }
    else
    {
        for(Polynomial poly = p; poly != null && p2 != null; poly = poly.link)
        {
            p2.data = (p2.data + poly.data);
            p2 = p2.link;
        }
    }
    return p2.head;
}

public float evaluate(float x)
{
    int i = head.length()-1;
    float y = 0;
    for(Polynomial poly = head; poly != null; poly = poly.link)
    {
        if(poly.link == null)
            y += poly.data;
        else
            y += (poly.data * (float)(Math.pow(x, i)));
        i -= 1;
    }
    return y;
}

@Override
public String toString()
{
    int i = 1;
    String polyString = "blank";
    for(Polynomial poly = head; poly != null; poly = poly.link)
    {
        if(polyString.equalsIgnoreCase("blank"))
        {
            if(poly.data != 0)
                    polyString = poly.data + "x^" + (poly.length()-i) + " + ";
            else if(poly.data == 1)
                polyString = "x^" + (poly.length()-i) + " + ";
            else
                polyString = poly.data + "x^" + (poly.length()-i) + " + ";
        }
        else
        {
            if(poly.link == null)
            {
                if(poly.data != 0)
                    polyString = polyString + poly.data;
                else if(poly.data == 1)
                    polyString = polyString + "x";
                else
                    polyString = polyString + poly.data + "x^" + (poly.length()-i);
            }
            else
            {
                if(poly.data != 0)
                    polyString = polyString + poly.data + "x^" + (poly.length()-i) + " + ";
                else if(poly.data == 1)
                    polyString = polyString + "x^" + (poly.length()-i) + " + ";
                else
                    ;
            }
        }
        i = i + 1;
    }
    return polyString;
}

public int length()
{
    int answer = 0;

    for(Polynomial poly = head; poly != null; poly = poly.link)
    {
        answer++;
    }
    return answer;
}

private static Polynomial insertAtFront(Polynomial head, float data)
{
    return new Polynomial(data, head);
}

}

I have a second class that is just a program to run these methods, and when I create a new Polynomial, and run associated methods, everything appears to run successfully. After I create a new Polynomial, the first Polynomial takes the second one’s values. I don’t understand 1. where the first-created polynomial’s values are going and 2. why it’s doing this at all.

Answer 1

protected static Polynomial head;

your head is declared as static – thus there is only one copy of it for all classes! Once your second Polynomial is created, it overrides the head of the first one.

You probably want it to be an instance variable and not a class variable.

Though, doing it will also have its own problems of infinite recursive constructor invokation. To overcome it, you might want to have a different class that holds a Polynomial head as an instance variable, and initialized it only once per list.