当我构造第二个新的多项式（链表）类时，第一个类采用第二个类的值

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);
}

}

我有第二个类，它只是一个运行这些方法的程序，当我创建一个新的多项式并运行关联的方法时，一切似乎都运行成功。创建新多项式后，第一个多项式采用第二个多项式的值。我不明白 1. 第一个创建的多项式的值将去往何处，以及 2. 为什么要这样做。

Answer 1

protected static Polynomial head;

您的 head 被声明为 static - 因此所有类都只有一份它的副本！创建第二个多项式后，它将覆盖第一个多项式的头部。

您可能希望它是实例变量而不是类变量。

但是，这样做也会带来无限递归构造函数调用的问题。为了克服这个问题，您可能需要一个不同的类，该类将多项式头作为实例变量，并且每个列表仅初始化一次。