多项式阵列不工作

Question

只是为了说明这一点，它是学校，所以我不寻找直接的答案只是有用的建议。我仅限于我可以使用的内置方法。基本上我要将一个多项式转换为数组p。然后再换成p1。最后将这些加在一起。出于某种原因，我得到错误“数组需要，但多项式找到”，我不知道为什么。老师也设置了返回双重价值，但我不确定为什么。忽略乘法部分。其他一切按预期工作。任何提示将不胜感激。

import java.util.Scanner; 
class Polynomial { 
    final int MAXSIZE = 20; 

    int p[]; //coefficient 
    int n; //degree 

    //array constructor 
    Polynomial() { 
     p = new int [MAXSIZE]; 
     n = -1; 
    } 

    void readP() { 
     Scanner in = new Scanner(System.in); 

     System.out.print("Enter degree: "); 
     n = in.nextInt(); 

     for (int i = 0; i <= n; i++) { 
      System.out.print("Enter a p[" + i + "]:"); 
      p[i] = in.nextInt(); 
      } 
     System.out.println(); 
    } 

    void printP() { 
     if (p[0] < 0) 
      System.out.printf("-"); 

     for (int i = 0; i < n; i++) 
      if (p[i] != 0) { 
       if (p[i] > 1) 
        System.out.printf(p[i] + "x^" + (n-i)); 
       else if (p[i] == 1) 
        System.out.printf("x^" + (n-i)); 

       if (p[i] < -1) 
        System.out.printf(p[i] * -1 + "x^" + (n-i)); 
       else if (p[i] == -1) 
        System.out.printf("x^" + (n-i)); 

       if (p[i+1] < 0) 
        System.out.printf(" - "); 
       else 
        System.out.printf(" + "); 
      } 
     if (p[n] > 0) 
      System.out.print(p[n]); 
     else 
      System.out.print(p[n] * -1); 
     System.out.println(); 
     System.out.println(); 
    } 

    double evalP(double x) { 
     int total = 0; 

     for (int i = n; i > 0; i--) 
      total += (p[i] * (Math.pow(x, i))); 
     total += p[n]; 
     System.out.println(); 
     return total; 
    } 

    double addP(Polynomial P1) { 
     for (int i = 0; i < n; i++) 
      p[i] = p[i] + P1[i]; 
     return total; 
    } 

    double multiplyP(Polynomial P1) { 
     for (int i = 0; i < n; i++) 
      p[i] += p[i] * P1[i]; 
     return p; 
    } 
} 

public class Lab5 { 
    public static void main(String[] args) { 
     Scanner in = new Scanner(System.in); 
     Polynomial myPoly = new Polynomial(); 
     String res; 
     Polynomial p1; 

     do { 
      System.out.println("1. Read Polynomial"); 
      System.out.println("2. Print Polynomial"); 
      System.out.println("3. Evaluate Polynomial"); 
      System.out.println("4. Add Polynomial"); 
      System.out.println("5. Multiply Polynomial"); 

      System.out.println("Q. Quit"); 

      System.out.print("Select: "); 
      res = in.next(); 
      System.out.println(); 

      switch (res.charAt(0)) { 
       case '1': 
        myPoly.readP(); 
        break; 
       case '2': 
        myPoly.printP(); 
        break; 
       case '3': 
        System.out.print("Enter x: "); 
        double x = in.nextDouble(); 
        System.out.print(myPoly.evalP(x)); 
        System.out.println(); 
        System.out.println(); 
        break; 
       case '4': 
        p1 = new Polynomial(); 
        p1.readP(); 
        myPoly.addP(p1); 
        break; 
       case '5': 
        p1 = new Polynomial(); 
        p1.readP(); 
        myPoly.multiplyP(p1); 
        System.out.println(); 
        System.out.println(); 
        break; 

       case 'Q': case 'q': 
        System.out.println("Bye!"); 
        break; 
       default: 
        System.out.println("Invalid!"); 
        System.out.println(); 
      } 
     } while (res.charAt(0) != 'Q' && res.charAt(0) != 'q'); 
    } 
} 

Answer 1

这两种方法都会按原样打破。正如azurefrog指出的那样，P1是一个Polynomial对象，不是一个Array，所以它不能处理括号语法。

double addP(Polynomial P1) {//P1 is a Polynomial 
    for (int i = 0; i < n; i++) 
     p[i] = p[i] + P1[i]; 
//can't use P1[i] syntax here. 
//Java will not guess that you intended to access the 'p' field of P1 
    return total; 
} 

double multiplyP(Polynomial P1) { 
    for (int i = 0; i < n; i++) 
     p[i] += p[i] * P1[i];//you'll probably have the same issue here as well 
    return p; 
} 

在使用括号语法之前，您需要访问多项式的数组字段'p'。如：

P1.p[i], not P1[i] 

这将使您：

double addP(Polynomial P1) { 
    for (int i = 0; i < n; i++) 
     p[i] = p[i] + P1.p[i]; 
    return total; 
} 

最后，如果你正在使用Eclipse或其他一些IDE，你可以设置一个断点一个异常，然后检查的数据它打破了。此外，你可以输入表达式，并确保你得到你所期望的。