Question

我似乎无法弄清楚我做错了什么。我试图返回数组D，但我得到的确切错误信息是：

Pa4.java:74: incompatible types
found   : double[]
required: double
return D;
       ^

我遇到问题的方法如下。

static double diff(double[] C){

  double D[];
  D = new double[(C.length-1)];
  for(int i = C.length; i > 0; i -= 1){
    int deg = 1;
    D[i] = deg * C[i];
    deg++;
  }

  for(int i = 0; i < C.length; i++){
    D[i] = C[i];
  }
  return D;
}

我的完整代码如下。它非常不完整，所以希望问题出现在我给出的第一个代码块中：

import java.util.Scanner;
import java.lang.Math;
class Pa4{



  public static void main(String[] args){

    Scanner sc = new Scanner(System.in);
    int degree;
    double C[];

    double resolution = 10^(-2);
    double threshhold = 10^(-3);
    double tolerance = 10^(-7);



    System.out.print("Enter the degree: ");
    degree = sc.nextInt();

    C = new double[degree];
    System.out.print("Enter "+(degree+1)+" coefficients: ");

    for(int i = 0; i < degree+1; i++){             // 1st number = last to enter
      C[i] = sc.nextInt();                         //stores coefficiant values in reverse order in an array
    }

    System.out.print("Enter the left and right endpoints: ");
    int a = sc.nextInt();                       
    int b = sc.nextInt();

    double x = findRoot(C, a, b, tolerance);
    double saf = poly(C, x);
    double sdf = diff(C);
    double asdf = poly(D, x);


  }


  static double poly(double[] C, double x){

    double sum = 0;
    for(int i = 0; i <= C.length; i =- i){
      int deg = 1;
      deg++;
      double hold = Math.pow(C[i], deg);
      hold = hold*x;
      sum = hold+sum;
    }
    return sum;
  }

  static double diff(double[] C){

    double D[];
    D = new double[(C.length-1)];
    for(int i = C.length; i > 0; i -= 1){
      int deg = 1;
      D[i] = deg * C[i];
      deg++;
    }

    for(int i = 0; i < C.length; i++){
      D[i] = C[i];
    }
    return D;
  }

  static double findRoot(double[] C, double a, double b, double tolerance){
    double x = 0; 
    double width = b-a;
    while(width > tolerance){
      x = (a + b)/2.0;
      if((a*a-2.0)*(x*x-2.0) < 0){
        b = x;
      }else{
        a = x;
      }
      width = b-a;
    }  
    return x;
               //use precondition (?)
  }
}

Answer 1

您的diff方法返回单个double，但您尝试返回double数组。将回复类型更改为double[]，并将通话更改为double[] sdf = diff(C);

BTW，您的diff方法还有其他问题：

D数组的长度为C.length - 1，但是您尝试将整个C数组分配给D.您将获得ArrayIndexOutOfBoundsException
该方法的大多数代码都没有意义，因为第二个循环将C的元素分配给D，因此方法的整个主体可以替换为return C。

我得到了错误：不兼容的类型＆＃39;当我尝试从方法中返回一个数组时

1 个答案: