java - 类预期错误。需要简单程序的帮助

Question

当我运行这个程序时，我收到以下错误:

Testscore.java:26: class expected
           grade = double.parseDouble(strInput);
                          ^
Testscore.java:26: ';' expected
           grade = double.parseDouble(strInput);
                                     ^
Testscore.java:26: not a statement
           grade = double.parseDouble(strInput);
                                      ^
Testscore.java:26: ';' expected
           grade = double.parseDouble(strInput);
                                              ^
4 errors

我的double.parseDouble(strInput);正确吗？

import javax.swing.*;
import java.lang.IllegalArgumentException;

public class Testscore
{
   public static void main(String[] args) 
    {
       int numberofTests = 0;

       double grade = new double[numberofTests];

       double startgrade = 0;

       String strInput;

    // Get how many tests are used

       strInput = JOptionPane.showInputDialog(null, "How many tests do you have? ");
       numberofTests = Integer.parseInt(strInput);

       grade = new double[(int) numberofTests];

       for (int index = 0; index < grade.length; index++)
       {
           strInput = JOptionPane.showInputDialog(null, "Enter Test Score." + (index + 1));
           grade = double.parseDouble(strInput);

           if (grade[index] < 0|| grade[index] > 100 )
           {   
               try 
                {
                   throw new InvalidTestScore();
                }

               catch (InvalidTestScore e)
               {
                   e.printlnStackTrace();
               }
           }   
       }

       for (int index = 0; index < grade.length; index++ )

            {
                startgrade += grade[index];
            }

            average = startgrade/grade.length;

            System.out.print("The average is: " + average);

    }
}

Answer 1

它是Double，大写D

请注意 double 和 Double 之间的区别。 “小” double 型是原始类型。另一个是类 - java.lang.Double。您可以在类上调用诸如 parseDouble(..) 之类的方法，而不是基元上的方法。 “big” double 也称为“包装类”，因为它将原始类型包装到一个类中。