当我构造第二个新的多项式(链表)类时，第一个类取第二个项式的值

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，一切似乎都成功运行。在我创建一个新的多项式后，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的去向和 2.为什么它这样做。

Answer 1

protected static Polynomial head;

您的head被声明为static - 因此所有类只有一个副本！创建第二个Polynomial后，它将覆盖第一个的头部。

您可能希望它是一个实例变量，而不是一个类变量。
但是，这样做也会有其无限递归构造函数调用的问题。为了克服它，您可能希望有一个不同的类，该类将Polynomial head作为实例变量保存，并且每个列表仅初始化一次。