Question

我已经完成了这个程序，除非我将价格或数量对象设置为负数而未设置为0.方向说如果价格不是正数，则应设置为0.0，如果数量不是正数，应该设置为0.以下是我的代码可以告诉我哪里出错了。

本练习是3.12发票类表格Deitel第10版如何编程：

public class Invoice {  
private String partNumber;
private String partDescription;
private int quantity;
private double priceperitem;
private double amount;  
public Invoice(String number, String partDescription, int quantity, double price)
{       
        this.partNumber = number;
        this.partDescription = partDescription;
        this.quantity = quantity;
        this.priceperitem = price;
}       
public void setPartNumber(String number)
{           
        partNumber = number;            
}       
public String getPartNumber()
{           
        return partNumber;
}   
public void setPartDescription (String description)
{           
        partDescription = description;
}       
    public String getPartDescription(){         
        return partDescription;         
    }   
    public void setQuantity(int count){         
        if(count > 0)
            quantity = 0;           
    }       
    public int getQuantity(){           
        return quantity;
    }   
    public void setPrice (double price){            
        if(price > 0.0)
            priceperitem = price;           
        if(price < 0.0)
            priceperitem = 0.0; 
    }       
    public double getPrice(){           
        return priceperitem;
    }   
    public double getInvoiceAmount(){           
         amount = getQuantity() * getPrice();           
         return amount;
    }       
}

import java.util.Scanner;
public class InvoiceTest {
public static void main(String[] args) {        
    int quantity;
    double price;
    double invoiceAmount;       
    Invoice invoice1 = new Invoice("1234","Hammer",-5, -39.75);     
    Scanner keyboard = new Scanner (System.in);     
    System.out.printf( "Part number: %s\n", invoice1.getPartNumber());
    System.out.printf( "Part Description: %s\n", invoice1.getPartDescription());
    System.out.printf( "Quantity: %s\n", invoice1.getQuantity());
    System.out.printf( "Price: %s\n", invoice1.getPrice());
 }
}

Answer 1

您正在检查条件，如果price<0然后将价格设置为0，则使用setter方法，即方法setPrice。但是你正在为价格建设者传递-ve论证，而这种建构者没有这样的检查。添加签入构造函数： -

public Invoice(String number, String partDescription, int quantity, double price)
{
    this.partNumber = number;
    this.partDescription = partDescription;
    this.quantity = quantity;

    if(price > 0.0)
     priceperitem = price;

    if(price < 0.0)
     priceperitem = 0.0; 

}

对于数量检查也是如此，在构造函数中以类似的方式添加数量检查。

另请注意，您在setQuantity中的条件无效，请将其更改为： -

  if(quantity > 0)
  this.quantity = price;

  if(quantity < 0)
  this.quantity = 0.0;

Answer 2

setQuantity方法正在执行无效检查。将if（count ＆gt; 0）更改为if（count ＆lt; 0）。即使在此更改之后，它也不起作用，因为您根本不使用set方法。您可以在构造函数中初始化变量时执行此操作，

public Invoice(String number, String partDescription, int quantity, double price)
{



    this.partNumber = number;
    this.partDescription = partDescription;
    **setQuantity(quantity);
    setPrice(price);**




}

Java Invoice程序 - 将数量设置为0设置为0.0

2 个答案: