Java 程序不工作答案

【问题标题】：Java program not workingJava 程序不工作
【发布时间】：2015-10-11 00:23:05
【问题描述】：

我的 java 程序无法正确计算折扣，我不知道为什么。我是java新手，我不知道如何解决这个问题，所以任何帮助都将不胜感激。例如，如果您购买 100 袋，您的折扣应该是 82.50，但我说的是 27.50

import java.text.DecimalFormat;
import java.util.Scanner;
public class Coffee {
    public static void main(String args[]){
        Scanner bags = new Scanner(System.in);
        System.out.println("Hello and welcome to the program");
        System.out.println("Here is the discount list for the IT125 Coffee Company");
        System.out.println("<= 24 Bags      No discount");
        System.out.println(">= 25 Bags      5% ");
        System.out.println(">= 50 Bags      10% ");
        System.out.println(">= 100 Bags     15% ");
        System.out.println(">= 150 Bags     20% ");
        System.out.println(">= 200 Bags     25% ");
        System.out.println(">= 300 Bags     30% ");
        System.out.println("");

        DecimalFormat df = new DecimalFormat("0.00");
        int num1;
        System.out.print("Enter the number of bags purchased: ");
        num1 = bags.nextInt();
        System.out.println("Bags purchased " + num1);
        double cost, disc, totcost;
        totcost = 0;
        disc = 0;
        cost = num1 * 5.50;
        System.out.println("Normal Price: € " + df.format(cost));



        if (num1 < 25) {
            System.out.println("Your dicount is " + disc);
            totcost = cost - disc;
            System.out.print("Your total cost is € " + df.format(totcost));
        }

        else if (num1 >= 25) {
            disc = cost * 0.05;
            totcost = cost - disc;
            System.out.println("Your dicount is € " + df.format(disc));
            System.out.print("Your total cost is € " + df.format(totcost));
        }

        else if (num1 >= 50) {
            disc = cost * 0.1;
            totcost = cost - disc;
            System.out.println("Your dicount is € " + df.format(disc));
            System.out.print("Your total cost is € " + df.format(totcost));
        }

        else if (num1 >= 100) {
            disc = cost * 0.15;
            totcost = cost - disc;
            System.out.println("Your dicount is € " + df.format(disc));
            System.out.print("Your total cost is € " + df.format(totcost));
        }

        else if (num1 >= 150) {
            disc = cost * 0.2;
            totcost = cost - disc;
            System.out.println("Your dicount is € " + df.format(disc));
            System.out.print("Your total cost is € " + df.format(totcost));
        }

        else if (num1 >= 200) {
            disc = cost * 0.25;
            totcost = cost - disc;
            System.out.println("Your dicount is € " + df.format(disc));
            System.out.print("Your total cost is € " + df.format(totcost));

        }

        else if (num1 >= 300) {
            disc = cost * 0.3;
            totcost = cost - disc;
            System.out.println("Your dicount is € " + df.format(disc));
            System.out.print("Your total cost is € " + df.format(totcost));
        }

    }

}

【问题讨论】：

您应该尝试将代码缩短为重现问题的最小示例。此外，显示所需的输出和问题输出。

标签： java

【解决方案1】：

万恶之源：

 else if (num1 >= 25) {

这会捕获从 25 到无穷大的所有数字。使用

 else if(num1 < 50) {

等等。将 300 以下的所有数量分开后，最后一个分支将不需要测试。

我想补充一点，代码重复不好。避免这种情况的一种方法是使用

int[] limit = new int[]{ 25, 50, 100, 150, 200, 300 };
int[] disct = new int[]{  5, 10,  15,  20, 25,   30 }

int d = 0;
for( int i = 0; i < limit.length; ++i ){ 
    if( qtty < limit[i] ) break;
    d = disct[i];
}

double cost = qtty*price;
double discount = cost*d/100;
totcost = cost - discount;

【讨论】：

要么这样，要么重新排序 if 语句，以便最大的数字在前。
...但绝不是两者兼而有之。

【解决方案2】：

您已将if 块按顺序排列，这样任何大于25 的块都会被第二个块捕获，即使它大到足以被后面的一个块捕获。 Java 不会检查else if 的列表；它几乎是一行一行的，所以如果它看到350 作为输入，它会看到它大于25 并进入那个if 块，即使它可以进入后面的块。如果您颠倒您的if 块的顺序，以便首先检查最大的数字，它将正常工作。

【讨论】：

【解决方案3】：

请尝试以下代码：添加边界条件。

import java.text.DecimalFormat;
import java.util.Scanner;
public class Coffee {
    public static void main(String args[]){
        Scanner bags = new Scanner(System.in);
        System.out.println("Hello and welcome to the program");
        System.out.println("Here is the discount list for the IT125 Coffee Company");
        System.out.println("<= 24 Bags      No discount");
        System.out.println(">= 25 Bags      5% ");
        System.out.println(">= 50 Bags      10% ");
        System.out.println(">= 100 Bags     15% ");
        System.out.println(">= 150 Bags     20% ");
        System.out.println(">= 200 Bags     25% ");
        System.out.println(">= 300 Bags     30% ");
        System.out.println("");

        DecimalFormat df = new DecimalFormat("0.00");
        int num1;
        System.out.print("Enter the number of bags purchased: ");
        num1 = bags.nextInt();
        System.out.println("Bags purchased " + num1);
        double cost, disc, totcost;
        totcost = 0;
        disc = 0;
        cost = num1 * 5.50;
        System.out.println("Normal Price: € " + df.format(cost));



        if (num1 < 25) {
            System.out.println("Your dicount is " + disc);
            totcost = cost - disc;
            System.out.print("Your total cost is € " + df.format(totcost));
        }

        else if (num1 >= 25 && num1<50) {
            disc = cost * 0.05;
            totcost = cost - disc;
            System.out.println("Your dicount is € " + df.format(disc));
            System.out.print("Your total cost is € " + df.format(totcost));
        }

        else if (num1 >= 50 && num1<100) {
            disc = cost * 0.1;
            totcost = cost - disc;
            System.out.println("Your dicount is € " + df.format(disc));
            System.out.print("Your total cost is € " + df.format(totcost));
        }

        else if (num1 >= 100 && num1<150) {
            disc = cost * 0.15;
            totcost = cost - disc;
            System.out.println("Your dicount is € " + df.format(disc));
            System.out.print("Your total cost is € " + df.format(totcost));
        }

        else if (num1 >= 150 && num1<200) {
            disc = cost * 0.2;
            totcost = cost - disc;
            System.out.println("Your dicount is € " + df.format(disc));
            System.out.print("Your total cost is € " + df.format(totcost));
        }

        else if (num1 >= 200 && num1<300) {
            disc = cost * 0.25;
            totcost = cost - disc;
            System.out.println("Your dicount is € " + df.format(disc));
            System.out.print("Your total cost is € " + df.format(totcost));

        }

        else if (num1 >= 300) {
            disc = cost * 0.3;
            totcost = cost - disc;
            System.out.println("Your dicount is € " + df.format(disc));
            System.out.print("Your total cost is € " + df.format(totcost));
        }

    }

}

输出：

Hello and welcome to the program
Here is the discount list for the IT125 Coffee Company
<= 24 Bags      No discount
>= 25 Bags      5% 
>= 50 Bags      10% 
>= 100 Bags     15% 
>= 150 Bags     20% 
>= 200 Bags     25% 
>= 300 Bags     30% 

Enter the number of bags purchased: 100
Bags purchased 100
Normal Price: € 550.00
Your dicount is € 82.50
Your total cost is € 467.50

【讨论】：

哦，废话，我试图给你投票，但现在它不允许我改变它。抱歉……

【解决方案4】：

我可以看到你的问题。

它在您的if/else 语句中。

假设您将 num1 设置为 60。您显然想执行下面的代码 C，但不幸的是，它将执行代码 B，因为它是第一个 if，导致 true：

这里：

   if (num1 < 25) {
     //A
   }
   else if (num1 >= 25) {
     //B
   }
   else if (num1 >= 50) {
     //C
   }

正确的if 块是：

   if (num1 < 25) {
     //A
   }
   else if (num1 >= 25 && num<50) {
     //B
   }
   else if (num1 >= 50) {
     //C
   }

这个例子没有你的那么多条件，你需要在你所有的if语句中加入下限和上限，除了最后一个。

【讨论】：

您只是推迟了错误的阈值。如果没有额外的预防措施，你就不能拥有num1 >= 50...
我知道还有更多 if 块，但我的解释应该是为了帮助 OP 理解问题，而不是为他们编写所有代码。
好的，但不要在答案中留下误导性代码 sn-ps。你有“正确的......将是”标题错误的代码，恕我直言，这是一个禁忌。