Question

error: incompatible types: String cannot be converted to double[]
      polyval = usrIn.nextLine();
                              ^
1 error

为什么这不起作用？我在做什么错了？

import java.util.Scanner; 

public class MainApp
{
   public static void main(String[] args){

      Scanner usrIn = new Scanner(System.in);
      double aval, bval, cval;

      System.out.println("Please enter infromation for three polynomials of type ax^2+bx+c.");

      System.out.println("Enter a, b, and c for polynomial 1:");

      double[] polyval = new double[3];
      polyval = usrIn.nextLine();

      System.out.println("Enter a, b, and c for polynomial 2:");
      double[] polyval2 = new double[3];
      //polyval2 = usrIn.nextLine();

      System.out.println("Enter a, b, and c for polynomial 3:");
      double[] polyval3 = new double[3];
      //polyval3 = usrIn.nextLine();
      System.out.println("Enter a, b, and c for polynomial 3:"
                         +"\t1. Print All Polynomials"
                         +"\t2.  Add Two Polynomials"
                         +"\t3. Factor Using Quadratic Formula"
                         +"\t4. Update a Polynomial"
                         +"\t5. Find Largest Polynomial"
                         +"\t6. Enter X and Solve"
                         +"\t7. Clear All Polynomials"
                         +"\t8. Exit the Program");
     }

}

  double[] polyval = new double[3];
  polyval = usrIn.nextLine();

我该如何解决

 error: incompatible types: String cannot be converted to double[]         
 polyval = usrIn.nextLine();
                             ^    
1 error

Answer 1

usrIn.nextLine()将返回一个字符串。如果要将其转换为double []，则需要首先通过在split上使用space来将字符串解析为数组（假设这是您输入的方式）。然后，对于数字的每个String表示形式，您都必须将其转换为double

    double[] polyval = new double[3];
    String[] nextLine = usrIn.nextLine().split(" ");

    for (int i = 0; i < nextLine.length; i++) {
      polyval[i] = Double.parseDouble(nextLine[i]);
    }

OR

    double[] polyval = new double[3];
    polyval = Arrays.stream(usrIn.nextLine().split(" ")).mapToDouble(Double::parseDouble).toArray();

这两种解决方案均未考虑到错误的输入，因此您将需要添加一些检查以确保输入的格式可接受。

例如：

在for循环之前，您可以添加支票

if (nextLine.length != 3) {
    System.out.println("input should have length of 3");
    System.exit(1);
}

字符串不能转换为double []

1 个答案: