java程序编译没有错误但无法运行

Question

这是我在 stackoverflow 成员建议的更改后的代码。代码编译时没有错误，但当我运行“java Realtor11”时，出现以下错误。我正在导入正确的库，所以不确定问题是什么。

该程序的目标是读取两个值(第一行是字符串 (John)，第二行是 double 值 (100))，并将它们与一些计算一起输出到 JOption 消息。

Exception in thread "main" java.lang.NullPointerException at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source) at java.lang.Double.parseDouble(Unknown Source) at Realtor11.main(Realtor11.java:49)

// java class for keyboard I/O
import java.util.Scanner;
// java class for JOption GUI
import javax.swing.JOptionPane;
// File reader
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;

public class Realtor11
{
    public static void main(String[] args)
    {
    // Keyboard and file input
        Scanner console = new Scanner(System.in); 
        Scanner inputStream = null;
    // price of the house, the cost to sell the house and the commission
        double price = 0;
        double cost, commission;
    // seller's name
        String seller = "name";



// GUI diplay message declaration
    String display_message = "This program calculates the cost to sell a home\n" 
    + "and the commission paid to an individual sales agent.\n\n"
    + "The user is asked for the last name of the seller and the\n"
    + "sales price.\n\n";

// Output descriptive messages
    JOptionPane.showMessageDialog(null, display_message, "Lab 1 Description", JOptionPane.INFORMATION_MESSAGE);

// Read Realtor11.txt
    try {
        BufferedReader in = new BufferedReader(new FileReader("Realtor11.txt"));
        while (in.read()!= -1);
        seller = in.readLine();
        price = Double.parseDouble(in.readLine());
        in.close();
        } 

        catch (IOException e) {}


// calculate the cost and the commission
    cost = 0.06 * price;
    commission = 0.015 * price;
// display the input and results
    String 
        out1 = String.format("%nThe " + seller + "'s" + " home sold for $%.2f%n", price),
        out2 = String.format("The cost to sell the home was $%.2f%n", cost),
        out3 = String.format("The selling or listing agent earned $%.2f%n", commission);

    JOptionPane.showMessageDialog(null, out1 + out2 + out3, seller + "'s Home Sale", JOptionPane.INFORMATION_MESSAGE);

// Output to file
// still writing this. 

}

}

Answer 1

问题出在这一行。

while (in.read()!= -1);

由于末尾有分号，这是一种“退化循环”。它继续从文件中读取，直到没有任何内容可供读取。之后，就没有要解析的 double 值了。