多项式类Java

Question

我试图为多项式类做两种方法，但我遇到了麻烦。第一种方法checkZeros应该检查多项式的系数中是否有前导零点。如果有前导零，该方法应该调整系数数组的大小。第二种方法应该找到多项式的导数，但我总是得到ArrayIndexOutOfBounds误差。

下面是它们：

public class Poly {

private float[] coefficients;
public static void main (String[] args){
    float[] fa = {3, 2, 4};
    Poly test = new Poly(fa);

}

public Poly() {
    coefficients = new float[1];
    coefficients[0] = 0;
}

public Poly(int degree) {
    coefficients = new float[degree+1];
    for (int i = 0; i <= degree; i++)
        coefficients[i] = 0;
}


public Poly(float[] a) {
    coefficients = new float[a.length];
    for (int i = 0; i < a.length; i++)
        coefficients[i] = a[i];
}

public int getDegree() {
    return coefficients.length-1;
}

public float getCoefficient(int i) {
    return coefficients[i];
}

public void setCoefficient(int i, float value) {
    coefficients[i] = value;
}

public Poly add(Poly p) {
    int n = getDegree();
    int m = p.getDegree();
    Poly result = new Poly(Poly.max(n, m));
    int i;

        for (i = 0; i <= Poly.min(n, m); i++) 
            result.setCoefficient(i, coefficients[i] + p.getCoefficient(i));
        if (i <= n) {
            //we have to copy the remaining coefficients from this object
            for ( ; i <= n; i++) 
                result.setCoefficient(i, coefficients[i]);
        } else {
            // we have to copy the remaining coefficients from p
            for ( ; i <= m; i++) 
                result.setCoefficient(i, p.getCoefficient(i));
        }
    return result;
}

public void displayPoly () {
    for (int i=0; i < coefficients.length; i++)
        System.out.print(" "+coefficients[i]);
    System.out.println();
}

private static int max (int n, int m) {
    if (n > m)
        return n;
    return m;
}

private static int min (int n, int m) {
    if (n > m)
        return m;
    return n;
}


public void checkForZeros(){
   int newDegree = getDegree();
   int length = coefficients.length;
   double testArray[] = coefficients;

   for (int i = length - 1; i >0; i--) {
      if (coefficients[i] != 0) {
       testArray[i] = coefficients[i];

        } 
   }

   for (int j = 0; j < testArray.length; j++){
       coefficients[j] = testArray[j];
   } 
}    


public Poly differentiate(){
   int n = getDegree();
   int newPolyDegree = n - 1;
   Poly newResult = new Poly();

   if (n == 0){
       newResult.setCoefficient(0, 0);
   }
   for (int i =0; i<= n; i++){
      newResult.setCoefficient(i, coefficients[i+1] * (i+1));
 }
   return newResult;
   }
}

Answer 1

我怀疑问题就在这里

   for (int i =0; i<= n; i++){
      newResult.setCoefficient(i, coefficients[i+1] * (i+1));
   }

既然是n = getDegree();，让我们假设多项式是1次的(例如1+x)。然后是n=1，我猜，系数的长度是2，但是你要检查系数2，它超出了界限。我猜你想

   for (i=0; i<=newPolyDegree; i++){
      newResult.setCoefficient(i, coefficients[i] * (i+1));
   }

或者别的什么..。很难用你给出的代码数量来判断。

Answer 2

您很可能得到了ArrayIndexOutofBounds，因为您以错误的方式实现了校验零，因此get自由度()返回的大小小于系数数组。考虑以下多项式：

f(x) = 2x^3 + 5x +1

系数数组将是

2,0,5,1

在检查结束后，它变成

2,5,1

我想程度函数仍将返回3，并且在differentiate()中将超出数组边界。

Answer 3

错误在循环中。

for (int i =0; i<= n; i++){
      newResult.setCoefficient(i, coefficients[i+1] * (i+1));

根据较少的信息，我假设: 1. setCoefficient( x的幂，x的系数)

在这种情况下，我们有一个n次微分多项式，它有n+1项，从0 -> n (x^0 -> x^n)开始，看循环，当i=n时，它必须取不存在的x^(n+1)系数。你应该这么做。

for (int i =0; i< n; i++){
      newResult.setCoefficient(i, coefficients[i+1] * (i+1));