Java 为什么我'；我无法计算销售金额和销售税金额？

您的发票号码是：1234。 你的销售额是：10.0。 你的销售税是：0.0。-----问题区域

----jGRASP wedge2:进程的退出代码为0。

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----jGRASP:操作完成。

您从未使用过

setSalePrice

方法，因此您的

SalesTax

参数从未被初始化。您可以这样初始化它：

double-SalesTax=salePrice*0.05
您从未调用setSalePrice，因此销售税从未设置

这里有一种方法可以纠正这一点，但实际上，您可能应该在调用displaySalePrice之前调用setSalePrice，而不是在其内部

public class Purchase
{

    int invoiceNumber = 1234;
    double salePrice = 10.00;
    double SalesTax;

    public void setInvoiceNumber(int invoice)
    {
        invoiceNumber = invoice;
    }

    public void setSalePrice(double saleAmount)
    {
        salePrice = saleAmount;
        SalesTax = (saleAmount * .05);//when I'm compiling it's not calculating

    }

    public void displaySalePrice()
    {
        System.out.println("Your invoice number is:" + invoiceNumber + ".");
        System.out.println("Your sale amount is: " + salePrice + ".");
        System.out.println("Your sales tax is: " + SalesTax + ".");
    }

 }

这会有用的

public void displaySalePrice()
{
    setSalePrice(salePrice);
    System.out.println("Your invoice number is:" + invoiceNumber + ".");
    System.out.println("Your sale amount is: " + salePrice + ".");
    System.out.println("Your sales tax is: " + SalesTax + ".");
}

注意这个类有一些风格上的问题


“SalesTax”以大写字母开头，应该为类（和接口）名称保留。正确的拼写是“销售税”

它缺少构造函数


示例构造函数：

public class Purchase
{

    int invoiceNumber = 1234;
    double salePrice = 10.00;
    double SalesTax = 0.0; // by default this is initialized to zero.

    public void setInvoiceNumber(int invoice)
    {
        invoiceNumber = invoice;
    }

    public void setSalePrice(double saleAmount)
    {
        salePrice = saleAmount;
        SalesTax = (saleAmount * .05);//when I'm compiling it's not calculating
    }

    public void displaySalePrice()
    {
        System.out.println("Your invoice number is:" + invoiceNumber + ".");
        System.out.println("Your sale amount is: " + salePrice + ".");
        System.out.println("Your sales tax is: " + SalesTax + ".");
    }

    public static void main(String args[]) 
    {
        setSalePrice(10.0); // sets SalesTax to (100.0 * .05)
        displaySalePrice();
    }

 }


购买是一种一旦完成就不会改变的东西。它的数据成员是可变的（可更改），但它们应该是不变的（最终或常量）


该类有setter（设置/更改变量），但缺少getter（在不更改变量的情况下检索变量值）。通常，变量应尽可能声明为“私有”和“最终”。所以如果我写这个类，我会这样写：


修订示例：

final int invoiceNumber; // These are set in the Constructor.
final double salePrice; // Once they are set, they don't change.
final double salesTax;

你能补充一些信息吗？您在哪里调用setSalePrice（双倍销售额）函数？
final int invoiceNumber; // These are set in the Constructor.
final double salePrice; // Once they are set, they don't change.
final double salesTax;

public class Purchase
{

    private final int invoiceNumber;
    private final double salePrice;
    private final double salesTax;

    // Constructor
    public Purchase(int invoiceN, double salesP) {
        invoiceNum = invoiceN;
        salesPrice = salesP;
        salesTax = salesPrice * .05; // The Constructor can figure this out.
    } 

    public int getInvoiceNumber()
    {
        return this.invoiceNumber; // "this." is optional
    }


    public double getSalePrice()
    {
        return this.salePrice();
    }

    public double getSalesTax()
    {
        return this.salesTax;
    }

    public void displaySalePrice()
    {
        System.out.println("Your invoice number is:" + getInvoiceNumber() + ".");
        System.out.println("Your sale amount is: " + getSalePrice() + ".");
        System.out.println("Your sales tax is: " + getSalesTax() + ".");
    }

    public static void main(String args[]) 
    {
        Purchase shoesPurchase = new Purchase(1234, 10.00);
        shoesPurchase.displaySalePrice();
    }

 }