是否有可能获得在公共多项式（double [] c）中建立的c的值抛出IllegalArgumentException？当我使用naiveEval方法时，我打印出值来检查它们是否到达。变量p和x都到达，但double [] c返回null。这有什么原因吗？我怎样才能解决这个问题？提前致谢！
public class PolynomialDemo {
public static int deg;
public static int deg2;
public static double x;
public static double x2;
public static double[] numbers;
public static double[] numbers2;
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
Polynomial pol = new Polynomial();
Polynomial pol2 = new Polynomial();
Scanner scan1 = new Scanner(System.in);
Scanner scan2 = new Scanner(System.in);
Scanner scan3 = new Scanner(System.in);
Scanner scan4 = new Scanner(System.in);
System.out.print("Enter the degree of the first polynomial -> ");
deg = scan1.nextInt();
System.out.print("Enter its coefficients in order of descending powers -> ");
String coe = scan2.nextLine();
String[] numbersStr = coe.split(" ");
double[] numbers = new double[ numbersStr.length ];
for ( int i = 0; i < numbersStr.length; i++ )
{
numbers[i] = Integer.parseInt( numbersStr[i] );
}
pol.setDegree(deg);
pol.setCoefficients(numbers);
System.out.println("f(x) = " + pol.toString());
System.out.println("deg f(x) = " + deg);
System.out.print("\nEnter the value of x at which the polynomial is to be evaluated -> ");
x = scan3.nextInt();
System.out.println("Using Horner’s method, f(" + x + ") = ");
System.out.println("Using naive method, f(" + x + ") = " + pol.naiveEval(x));
System.out.print("\nEnter the degree of the second polynomial -> ");
deg2 = scan1.nextInt();
System.out.print("Enter its coefficients in order of descending powers -> ");
String coe2 = scan2.nextLine();
String[] numbersStr2 = coe2.split(" ");
double[] numbers2 = new double[ numbersStr2.length ];
for ( int i = 0; i < numbersStr2.length; i++ )
{
numbers2[i] = Double.parseDouble( numbersStr2[i] );
}
pol2.setDegree(deg2);
pol2.setCoefficients(numbers2);
System.out.println("f(x) = " + pol2.toString());
System.out.println("deg f(x) = " + deg2);
System.out.print("\nEnter the value of x at which the polynomial is to be evaluated -> ");
x2 = scan4.nextInt();
System.out.println("Using Horner’s method, f(" + x2 + ") = ");
System.out.println("Using naive method, f(" + x2 + ") = ");
}
}
然后是我的多项式课程
public class Polynomial implements PolyEval {
private double[] coeffs;
private int degree;
private double p;
private double[] c;
public void setDegree(int degree){
this.degree = degree;
}
public void setCoefficients(double[] coeffs){
this.coeffs = coeffs;
}
public Polynomial() {
p = 0;
}
public Polynomial(double[] c) throws IllegalArgumentException{
c = this.coeffs.clone();
if (c[0] == 0)
throw new IllegalArgumentException("Zero, try again");
if (c.length > 1)
throw new IllegalArgumentException("Greater than 1");
}
@Override
public double hornerEval(double x) {
throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}
@Override
public double naiveEval(double x) {
System.out.println(Arrays.toString(c));
double y = coeffs[degree()];
for(int k = degree()-1; k >= 0; k--)
{
p++;
double t = 1;
for(int j = 1; j <= p; j++)
{
t*=x;
}
y += coeffs[k]*t;
}
return y;
}
@Override
public int degree() {
return this.degree;
}
@Override
public String toString() {
if (this.degree == -1) return "0";
else if (this.degree == 0) return "" + this.coeffs[0];
else if (this.degree == 1) return this.coeffs[0] + "x +" + this.coeffs[1];
String s = this.coeffs[0] + "x^" + degree;
for (int i = 1; i <= this.degree; i++) {
if (this.coeffs[i] == 0) continue;
else if (this.coeffs[i] == 1) s = s + " + ";
else if (this.coeffs[i] == -1) s = s + " - ";
else if (this.coeffs[i] > 0) s = s + " + " + ( this.coeffs[i]);
else if (this.coeffs[i] < 0) s = s + " - " + (-this.coeffs[i]);
if (i == this.degree-1) s = s + "x";
else if (i == this.degree) s = s;
else if (i >= 1) s = s + "x^" + (this.degree-i);
}
s = s.replaceAll("([0-9])\\.0+([^0-9]|$)", "$1$2");
return s;
}
}
答案 0 :(得分：-1)
public Polynomial(double[] c)是您方法的构造函数。
构造函数中的第一个语句是：
c = this.coeffs.clone();
这意味着您将作为constructors参数传入的变量c中当前保存的值替换为this.coeffs.clone()
由于您的代码示例未显示字段coeffs的声明位置和方式，因此我假设它尚未初始化。
coeffs在另一个类中定义并初始化。如果我打印出coeffs我得到了数组，但是当我尝试将coeffs复制到c时，c不会从该方法打印出数组。 - 戴尔
根据您提供的示例，这必须是您未展示的Polynomial的超类。
您也未能提供Minimal, Complete, and Verifiable example (MCVE)。
因此，我认为打印'coeffs'的“检查”可能有效，因为它是通过直接实例化超类来完成的，这不是有效的证明。
忽略构造函数参数并立即替换它的值本身就是一个错误，也是我视图中问题的根本原因。