我不明白为什么我的计算不起作用

Question

我对编程很陌生。这是carHire类。两个人中有一个。我已经要求开发一个基于GUI的汽车租赁应用程序。所以当我输入一个条目时，一切看起来都很好，但是我的租金仍然是0。我搞不懂。

公共类CarHire {

    private String customerName;
    private String licenseNumber;
    private int daysHired;

        CarHire(){
            customerName=null;
            licenseNumber=null;
            daysHired=0;
            }
        CarHire(String customerName, String licenseNumber, int daysHired){
            this.customerName = customerName;
            this.licenseNumber = licenseNumber;
            this.daysHired = daysHired;
            }
            public void setCustomerName(String customerName){
                this.customerName = customerName;
            }
            public void setLicenseNumber(String licenseNumber){
                this.licenseNumber = licenseNumber;
            }
            public void setDaysHired(int daysHired){
                this.daysHired = daysHired;
            }

            public String getCustomerName()
            {
                return customerName;
            }
            public String getLicenseNumber()
            {
                return licenseNumber;
            }
            public int getDaysHired()
            {
                return daysHired;
            }

    public double calculateHireRental(){
        final double BASE_RATE = 34.5;
    final double NEXT_TIER_RATE = 30.5;
    final double LAST_TIER_RATE = 22.5;

    final int NEXT_TIER_START_DAY=4;
    final int LAST_TIER_START_DAY=7;

    double rental= 0.0;
        int days = 0;

    if(days<NEXT_TIER_START_DAY){   
            rental=days*BASE_RATE;
     } 
        else if(days<=LAST_TIER_START_DAY){
            rental=3*BASE_RATE+(days-3)*NEXT_TIER_RATE;
        }
        else{
    rental=3*BASE_RATE+4*NEXT_TIER_RATE+(days-7)*LAST_TIER_RATE;
        }
        return rental;
    }
}`

下面是GUI类。

//进程输入数据

            `public void enterData()
            {
          if (nameField.getText().compareTo("") == 0)
                {
                    JOptionPane.showMessageDialog(null,"You must enter a customer name","XYZ Car Hire App",JOptionPane.ERROR_MESSAGE);
                    return;
                }
                if (licenseField.getText().compareTo("") == 0)
                {
                    JOptionPane.showMessageDialog(null,"You must enter a license number","XYZ Car Hire App",JOptionPane.ERROR_MESSAGE);
                    return;
                }
                if (daysField.getText().compareTo("") == 0)
                {
                    JOptionPane.showMessageDialog(null,"You must enter days hired","XYZ Car Hire App",JOptionPane.ERROR_MESSAGE);
                    return;
                }
                //if (currentCustomer == MAX_NUM)


                                String customerName = nameField.getText();
                                String licenseNumber = licenseField.getText();
                                int daysHired = Integer.parseInt(daysField.getText());

                                displayHeading();
                                CarHire g = new CarHire(customerName,licenseNumber,daysHired);

                    carHireArray[currentCustomer] = g;

                    textArea.append(String.format("%-25s%-28s%-32s$%3.2f\n",customerName, licenseNumber, daysHired, g.calculateHireRental()));






            if (enterButton.isEnabled())//todo-- clear textfields and return focus
                {
                                nameField.setText("");
                nameField.requestFocus();

                licenseField.setText("");
                licenseField.requestFocus();

                daysField.setText("");
                daysField.requestFocus();

        }
                currentCustomer++;//todo-- incremental current cusomer number
        }     
        // Display all bookings
    public void displayAll()
    {
                textArea.setText("");

                displayHeading();
           //todo-- call displayHeading() method
                for(int i=0;i<MAX_NUM;i++)
        {
            CarHire listCustomer = carHireArray[i];

                        textArea.append(String.format("%-25s%-22s%-28s$%3.2f\n",listCustomer.getCustomerName(), listCustomer.getLicenseNumber(), listCustomer.getDaysHired(), listCustomer.calculateHireRental()));
        }//todo-- display all entries entered so far (need using a loop)
                            //todo-- display number of entries, average days hired, total rental
                    if (nameField.getText().compareTo("") == 0)
                    {
            JOptionPane.showMessageDialog(null,"No customer entered","XYZ Car Hire App",JOptionPane.ERROR_MESSAGE);
                    }//todo-- complete error message

    }`

Answer 1

在calculateHireRental()中有int days = 0;，所以第一个if是真的，并且返回days * BASE_RATE，即0。

删除days变量并使用类成员daysHired。

Answer 2

在您提供的代码中:在GUI中，将结果赋值给'daysHired‘变量

        int daysHired = Integer.parseInt(daysField.getText());

但是，在类CarHire中，变量天数已经预定义为0：

int days = 0;  

因此，无论你把多少乘以“天”(乘以0)，你都会得到0：

 rental=days*BASE_RATE;

Answer 3

看起来您总是设置days =0 ...look up