Java 如何更改扫描仪的输入

我有点困在这里了。目前我正在为学校做一个项目。我最近发现代码应该从文件中读取，而不是从用户输入中读取。我有没有办法改变我的流程？我需要它读取的文件是quartlyemployeedata.txt 这是我的主要课程：

MonthlyPayroll.java

import java.util.*;

class MonthlyPayrollDriver
{
    private static final int WORKFORCE_SIZE = 3;
    private static Scanner inputScan;

    public static void main (String[] args)
    {

        // Set up array of employees
        // Note the objects in the array could be in subclasses of Employee
        Employee[] employeeList = new Employee[WORKFORCE_SIZE];

        inputScan = new Scanner(System.in);

        for(int empNum = 0; empNum < WORKFORCE_SIZE; empNum++)
        {
            System.out.print("Enter employee first name and last name: ");
            String first = inputScan.next();
            String last = inputScan.next();
            System.out.print("\nPlease determind the Status code (F for full-time, P for part time, and I for intern) ");
            char response = inputScan.next().charAt(0);
            {

            if (response == 'f' || response == 'F')
            {
                System.out.print("\nPlease determind the Status Code (S for salaried or H for hourly) ");
                {
                    char response1 = inputScan.next().charAt(0);
                    if (response1 == 'h' || response1 == 'H')
                    {
                        System.out.print("\nEnter hourly rate: ");
                        double hourlyRate = inputScan.nextDouble();
                        System.out.print("\nEnter hours worked last Month: ");
                        inputScan.nextDouble();
                        employeeList[empNum] = new HourlyEmployee(last,first,hourlyRate);
                    }
                    char response2 = inputScan.next().charAt(0);
                    if (response2 == 's' || response2 == 'S')
                    {
                        System.out.print("Enter annual salary: ");
                        double annualPay = inputScan.nextDouble();
                        employeeList[empNum] = new SalariedEmployee(last,first,annualPay);
                    }
                }

            }

            if (response == 'p' || response == 'P') 
            {
                System.out.print("\nEnter hourly rate: ");
                double hourlyRate = inputScan.nextDouble();
                System.out.print("\nEnter hours worked last month: ");
                inputScan.nextDouble();
                employeeList[empNum] = new HourlyEmployee(last, first,
                        hourlyRate);

            }

            if (response == 'i' || response == 'I')
            {
                System.out.print("\nPlease determind the Status Code (H for hourly or U for unpaid.) ");
                {
                    char response1 = inputScan.next().charAt(0);
                    if (response1 == 'H' || response1 == 'h') 
                    {
                        System.out.print("\nEnter hourly rate: ");
                        double hourlyRate = inputScan.nextDouble();
                        System.out.print("\nEnter hours worked last month: ");
                        inputScan.nextDouble();
                        employeeList[empNum] = new HourlyEmployee(last, first,
                                hourlyRate);
                    }

                    else 
                    {
                        employeeList[empNum] = new HourlyEmployee(last,first,0);
                    }
                }
            }
        }
    }

        System.out.println("\n\nMonthly Payroll\n");
        for(int j = 0; j < WORKFORCE_SIZE; j++)
        {
            System.out.println(employeeList[j]);
        }

    }

}

当然，找零

inputScan = new Scanner(System.in);

到

其中filePath是您需要读取的文件的路径。javadoc说

构造一个新的扫描仪，该扫描仪生成从指定文件扫描的值

---

这是使您的程序从标准输入（默认为控制台）读取的原因：

inputScan = new Scanner(System.in);

您可以通过两种方式进行更改：

使用操作系统特定语法创建文件，或 创建从文件读取的扫描仪。 第一个选项是这样做的：

java MonthlyPayrollDriver <my_input_file.txt

File file = new File("my_input_file.txt");
inputScan = new Scanner(file);

---

对于第一个选项，我要更改什么才能使其工作？@开始时，您不需要更改任何内容使第一个选项工作，甚至不需要重新编译。@开始时，您这样运行它时会发生什么？你有错误吗？你有什么收获吗？试着在调试器中运行它，逐步检查代码，看看发生了什么。我正在尝试第二种方法，因为我意识到我会使用它。现在，我在MonthlyPayrollDriver.mainMonthlyPayrollDriver.java:29的线程main java.lang.NullPointerException中遇到异常，因为某些原因，它没有拾取文件。如果它位于不同计算机的不同位置，又会怎样

File file = new File("my_input_file.txt");
inputScan = new Scanner(file);