Java：麻烦调用另一个类

Question

I am just beginning in Java and I am having a peculiar problem that I just cant seem to get to the root of. I have 2 programs and one is taking data from a text file and then calling it into a class to do some calculations and finally putting the output into another text document.

Everything works except this part here:

public class Paycheck
{
//Constants for the private class
private final String EMPLOYEE_NAME;           //Employee name          
private final String SOC_SEC_NUM;             //Employee Social Security Number
private final double WAGE_RATE;               //Employee wage
private final double TAX_RATE;                //Employee tax withheld 
private final double HOURS_WORKED;            //Employee's hours of work

//Variables for the private class
private double grossPay;                      //Employee Gross Pay
private double taxWithheld;                   //Employee Tax Withheld
private double netPay;                        //Employee Net Pay





//This is the constructor. It is called whenever an instance of the class is created
public Paycheck (String name, String ssn, double wage, double tax, double hours)
{
    EMPLOYEE_NAME = name;  //Instance employee name
    SOC_SEC_NUM = ssn;    //Instance employee SSN
    WAGE_RATE = wage;      //Instance employee wage rate
    TAX_RATE = tax;        //Instance employee tax rate
    HOURS_WORKED = hours;  //Instance employee hours worked
}

//This calculates the variables in the paycheck class
public void calcWages()
{
    grossPay = WAGE_RATE * HOURS_WORKED;    //Calculates Gross Pay
    taxWithheld = grossPay * TAX_RATE;      //Calculates Taxes Withheld
    netPay = grossPay - taxWithheld;        //Calculates net pay

}




//Returns the Paycheck objects Employee Name
public String getEmployeeName()
{
    return EMPLOYEE_NAME;
}

//Returns the employee SSN of the Paycheck object
public String getSocSecNum()
{
    return SOC_SEC_NUM;
}

//Reeturns a Paycheck object's employee Wage Rate
public double getWageRate()
{
    return WAGE_RATE;
}

//Returns a Paycheck object's employee tax rate
public double getTaxRate()
{
    return TAX_RATE;
}

//Returns an Paycheck object's employee hours worked
public double getHoursWorked()
{
    return HOURS_WORKED;
}

//Returns a Paycheck object's gross pay
public double getGrossPay()
{
    return grossPay;
}

//Returns a Paycheck object's Taxes Withheld
public double getTaxWithheld()
{
    return taxWithheld;
}

//Returns a paycheck object't net pay 
public double getNetPay()
{
    return netPay;
}

The calcWages() does the necessary calculations and below this are a series of get statements to call them. However, my output does not return any values for the calcWages() arguments.

I added the getters here and my other program is grabbing them. However the final output on my other program is coming up as 0.

Where am I going wrong here?

This is the part of the main method that is calling them

  public static void main(String [] args) throws IOException //Throws clause
{
    //Declare constants
    final String INPUT_FILE = "Employee.txt";         //Input text file containing Employee information
    final String OUTPUT_FILE= "PayrollHistory.txt";   //Output text file that will receive the data

    //Declare Variables
    String payPeriodDate;       //Ending date of the pay period
    String employeeName;        //Employee Name in text file
    String employeeSocSecNum;   //Employee SSN in text file
    double employeeHours;       //Employee hours worked
    double employeeTax;         //Employee Tax rate 
    double employeeWage;        //Employee Wage rate
    double totalGrossPay;       //Total employee Gross for pay period
    double totalTaxWithheld;    //Total Tax Withheld for pay period
    double totalNetPay;         //Total Net Payroll for pay period
    String input;               //String input for double conversion in JoptionPane

    DecimalFormat money = new DecimalFormat ("#0.00"); // Decimal Format to put money in the right format(USD)

    //This ensures that the input file actually exists in the program folder 
    //And exits the program if it does not, along with the prompt.
    File file = new File(INPUT_FILE);
  if (!file.exists())
  {
     JOptionPane.showMessageDialog(null, "The " + INPUT_FILE + " file cannot be found." +
                        "Program terminated.");
     System.exit(0);
  }


    // Create Scanner object to enable reading data from input file
  Scanner inputFile = new Scanner(file);

  // Create FileWriter and PrintWriter objects to enable
  // writing (appending not overwriting) data to text file
  FileWriter fwriter = new FileWriter(OUTPUT_FILE, true);
  PrintWriter outputFile = new PrintWriter(fwriter);

    //Initialize accumulator values
  totalGrossPay = 0.0;
    totalTaxWithheld = 0.0;
    totalNetPay = 0.0;

    //Get the pay period for the employee
    payPeriodDate = JOptionPane.showInputDialog("Enter pay period ending date (mm/dd/yyyy):");
    outputFile.println("PAY PERIOD ENDING DATE: " + payPeriodDate);          //Inputs pay period date into the text file
    outputFile.println(); // Blank line
    outputFile.println(); // Blank line


    while (inputFile.hasNext()) // This will look through the input file and get the necessary variable input
  {
     // Read employee Name from Input File
     employeeName = inputFile.nextLine();
     // Read employee SSN from input file
     employeeSocSecNum = inputFile.nextLine();
     // Read employee Wage Rate from input file
        //Parses it into a double type
     input = inputFile.nextLine();
     employeeWage = Double.parseDouble(input);
        //Read employee tax rate from input file
        //Parses it into a double type
        input = inputFile.nextLine();
        employeeTax = Double.parseDouble(input);


        //Get number of hours worked
        input = JOptionPane.showInputDialog("Employee Name: " + employeeName +
                                                        "\nEnter number of hours worked:");
        employeeHours = Double.parseDouble(input);

        //This call the paycheck class to create a new Paycheck Object
        Paycheck employee = new Paycheck (employeeName, employeeSocSecNum, employeeWage, employeeTax, employeeHours);

        // Call Paycheck class methods into the output file
     outputFile.println("Employee Name: " + employeeName);                              //Employee Name
     outputFile.println("SSN: " + employeeSocSecNum);                                   //Employee SSN
     outputFile.println("Hours Worked: " + employeeHours);                              //Employee Hours Worked
     outputFile.println("Wage Rate: " +  money.format(employeeWage));                   //Employee Wage Rate
        outputFile.println("Gross Pay: " +  money.format(employee.getGrossPay()));         //Employee Gross Pay
        outputFile.println("Tax Rate: " +  money.format(employeeTax));                     //Employee Tax Rate
        outputFile.println("Tax Withheld: " +  money.format(employee.getTaxWithheld()));   //Employee Tax Withheld
        outputFile.println("Net Pay: " + employee.getNetPay());                            //Employee Net Pay
     outputFile.println(); // Blank line

Answer 1

You don't appear to be actually calling calcWages() before calling your getters, so grossPay, taxWithheld, and netPay are still going to be 0, as that's Java's default value for uninitialized numbers.

You need to call employee.calcWages() before referencing those values for them to change.

Answer 2

It is because calcWages() is declared void ( public void calcWages() ), meaning it is not supposed to return any value but just complete a series of steps (calc payroll particulars in this example). After calling it, just proceed to reference the instance variables it processed.

Answer 3

您已将变量声明为final ，这意味着它们只能分配一次。