故障調用和使用Java方法

Question

我剛開始學習Java，並試圖根據作業表編寫一個程序（在該帖子的底部給出了此表）。但是，我真的不太明白如何使用方法。我已經在「Customer.java」類中編寫了方法，並且正在嘗試在「TestCustomer.java」類中使用它們。但是，因爲我真的不知道如何做到這一點，所以它變得非常可怕。我在這方面搜索了一些信息，但我似乎一直在讓自己更加困惑。你們有沒有機會向我展示使用這些方法的正確方法，或者至少讓我指出正確的方向？非常感謝您提供的任何幫助。

Customer類

import java.util.Scanner; 

import javax.swing.JOptionPane; 


public class Customer { 
public static double taxRate = 0.00; 
public static double saleRate = 0.00; 
String customerName; 
double listSaleAmount; 
double saleDiscount = 0; 
double netSaleAmount; 
double taxAmount; 
double saleTotal; 
boolean taxable; 

public Customer (String CustomerName, boolean taxable) { 

} 

public double calculateTax (double listSaleAmount) { 
    saleDiscount = listSaleAmount*saleRate; 
    netSaleAmount = listSaleAmount-saleDiscount; 
    if (taxable == true) { 
    taxAmount = netSaleAmount*taxRate; 
    } 
    else { 
    taxAmount = 0.00; 
    } 
    saleTotal = listSaleAmount + taxAmount; 


    return saleTotal; 

} 

public String printRecord; { 
    System.out.println("Customer is " + customerName); 
    System.out.println("Sale amount is $" + listSaleAmount); 
    System.out.println("Discount amount is $" + saleDiscount); 
    System.out.println("Net Sale Amount is $" + netSaleAmount); 
    System.out.println("Tax amount is $" + taxAmount); 
    System.out.println("Total Sale Amount is $" + saleTotal); 
} 

public static double changeTaxAmount (double taxRate) { 
    Scanner input = new Scanner(System.in); 
    double userTaxAmount = Double.parseDouble(JOptionPane.showInputDialog("What is the Tax Rate? (8.25 & 8.50 for testing)")); 
    taxRate = userTaxAmount; 
    return taxRate; 

} 

public static double changeSaleRate (double saleRate) { 
    Scanner input = new Scanner(System.in); 
    double userSaleAmount = Double.parseDouble(JOptionPane.showInputDialog("What is the Sale Discount Rate? (0.00 & 7.50 for testing)")); 
    saleRate= userSaleAmount; 
    return saleRate; 
} 

public static String printTaxRate; { 
    System.out.println("Tax Rate is" + taxRate + "%."); 
} 

public static String printSaleRate; { 
    System.out.println("The Sale Rate is" + saleRate + "."); 
} 
} 

TestCustomer類

import java.math.BigDecimal; 
public class TestCustomer { 

    /** 
    * @param args 
    */ 
    public static void main(String[] args) { 
     // TODO Auto-generated method stub 

Customer customer1 = new Customer("Annie Smith", true); 
Customer customer2 = new Customer("Bob Wilson", false); 
Double totalOfAllSales = 0.00; 


//I have no clue how to actually use the methods I created in the Customer class! 
//These are my best guesses, which are obviously wrong 
//Any help here would be greatly appreciated! 
Customer.changeTaxAmount(taxRate); 

Customer.printTaxRate; 

Customer.changeSaleRate(saleRate); 

Customer.printSaleRate; 

customer1.listSaleAmount = 65.00; 
customer2.listSaleAmount = 52.00; 

totalOfAllSales += customer1.calculateTax; 
totalOfAllSales += customer2.calculateTax; 

customer1.printRecord; 
customer2.printRecord; 

Customer.changeTaxAmount(taxRate); 
Customer.printTaxRate; 
Customer.changeSaleRate(saleRate); 
Customer.printSaleRate; 

customer1.listSaleAmount = 84.00; 
customer2.listSaleAmount = 105.00; 
totalOfAllSales += customer1.calculateTax; 
totalOfAllSales += customer2.calculateTax; 
customer1.printRecord; 
customer2.printRecord; 

System.out.println("The total of all sales is $" + totalOfAllSales); 
    } 

} 

分配表（不擔心現在打印到文件，只是想主要機械工作）

Answer 1

您似乎對調用方法的語法感到困惑。語法如下：

object.method(arguments) 

如果沒有參數，它看起來像這樣：

object.method() 

另外，你需要像你這樣在這裏使用存取和突變的方法，而不是直接設置實例變量：

customer1.listSaleAmount = 65.00; 

你應該實現這樣的方法：

public void setListSaleAmount(double lsa) { 
    listSaleAmout = lsa; 
} 

public double getListSaleAmount() { 
    return listSaleAmount; 
} 

and make listSaleAmount private。

問題＃2：定義方法的語法。你正使用該代碼來定義的方法：

public static String printTaxRate; { 
    System.out.println("Tax Rate is" + taxRate + "%."); 
} 

您應該使用此代碼：

public static String printTaxRate() { 
    System.out.println("Tax Rate is" + taxRate + "%."); 
} 

的問題是該方法首部內的古怪放置分號。