简单折扣

Question

备考遇到问题，我是初学者。它是一个折扣计算器。一袋咖啡售价 3.75 欧元 10 袋或以上 5% 折扣 20袋以上立减10%

到目前为止我有什么

import java.util.Scanner;
public class discount {
public static void main (String[] args){

//Scanner input; Keep this as one line. It is good practice
Scanner input = new Scanner(System.in);
double bag;
double discount;
double cost = 3.75;

//Input = new Scanner(System.ini);     combined with line above.
System.out.println("Enter Numer of bag");
bag = input.nextDouble();
//If (bag ==>10&&<20) × .05  incorrect Java syntax

if(bag >= 10 && < 20) {
 discount = 0.05;
}
else if(bag >= 20) {
  discount = 0.10;
} 
else {
  discount = 0;
}

double finalPrice;
finalPrice = (cost * bag) * (1 - discount);

System.out.println("You ordered " + bag + " bags of coffee.");
System.out.println("Your dicount is " + discount + "%");
System.out.println("You total is: " + finalPrice);

} }

Answer 1

我通常不赞成给 Tom Sawyer 的学生做作业，但在这种情况下，我认为对于任何学会以不同方式看待问题的初学者来说，都有教育机会。

这是一个简单的class，但是如果你想成为一名程序员，养成良好的习惯是个好主意。

非常注意代码格式和可读性。仔细考虑 class 元素、方法和变量的名称。如果名称不言自明，您需要的注释就更少了。

学习并关注 Java coding standards。这将有助于提高可读性。

忘记输入和输出以及用户界面 - 首先获得正确的功能。

import java.util.LinkedHashMap;
import java.util.Map;

/**
 * CoffeePriceCalculator
 * User: mduffy
 * Date: 7/22/2016
 * Time: 7:46 AM
 * @link 
 */
public class CoffeePriceCalculator {

    // Is double a good way to represent money?  What about units?  Conversions?
    public static final double DEFAULT_UNIT_PRICE = 3.75;  // British pounds

    private static final Map<Integer, Double> DISCOUNT_PERCENTAGE;

    static {
        DISCOUNT_PERCENTAGE = new LinkedHashMap<>();
        DISCOUNT_PERCENTAGE.put(10, 0.05);
        DISCOUNT_PERCENTAGE.put(20, 0.10);
    }

    public double calculatePrice(int numBags, double unitPrice) {
        if (numBags < 0) throw new IllegalArgumentException("Number of bags must be positive");
        if (unitPrice < 0.0) throw new IllegalArgumentException("Unit price must be positive");
        double price = numBags*unitPrice;
        price -= calculateDiscount(numBags, price);
        return price;
    }

    public double calculatePrice(int numBags) {
        return this.calculatePrice(numBags, DEFAULT_UNIT_PRICE);
    }

    public double calculateDiscount(int numBags, double price) {
        if (numBags < 0) throw new IllegalArgumentException("Number of bags must be positive");
        if (price < 0.0) throw new IllegalArgumentException("Total price must be positive");
        double discount = 0.0;
        for (int minBags : DISCOUNT_PERCENTAGE.keySet()) {
            if (numBags >= minBags) {
                discount = price*DISCOUNT_PERCENTAGE.get(minBags);
                break;
            }
        }
        return discount;
    }
}

现在学习 JUnit 和测试驱动开发并不算早。

import org.junit.Assert;
import org.junit.Test;

/**
 * Junit test for CoffeePriceCalculator
 * User: mduffy
 * Date: 7/22/2016
 * Time: 7:50 AM
 * @link 
 */
public class CoffeePriceCalculatorTest {

    public static final double TOLERANCE = 1.0e-3;

    @Test
    public void testCalculatePrice_NoDiscount() {
        // setup
        CoffeePriceCalculator coffeePriceCalculator = new CoffeePriceCalculator();
        int numBags = 5;
        // exercise
        double actual = coffeePriceCalculator.calculatePrice(numBags);
        // assert
        Assert.assertEquals(numBags * CoffeePriceCalculator.DEFAULT_UNIT_PRICE, actual, TOLERANCE);
    }

    @Test
    public void testCalculatorPrice_LowDiscount() {
        // setup
        CoffeePriceCalculator coffeePriceCalculator = new CoffeePriceCalculator();
        int numBags = 15;
        // exercise
        double actual = coffeePriceCalculator.calculatePrice(numBags);
        // assert
        Assert.assertEquals(numBags * CoffeePriceCalculator.DEFAULT_UNIT_PRICE*0.95, actual, TOLERANCE);
    }

    @Test
    public void testCalculatorPrice_HighDiscount() {
        // setup
        CoffeePriceCalculator coffeePriceCalculator = new CoffeePriceCalculator();
        int numBags = 25;
        // exercise
        double actual = coffeePriceCalculator.calculatePrice(numBags);
        // assert
        Assert.assertEquals(numBags * CoffeePriceCalculator.DEFAULT_UNIT_PRICE*0.90, actual, TOLERANCE);
    }

    @Test(expected = IllegalArgumentException.class)
    public void testCalculatePrice_NegativeBags() {
        // setup
        CoffeePriceCalculator coffeePriceCalculator = new CoffeePriceCalculator();
        int numBags = -25;
        // exercise
        coffeePriceCalculator.calculatePrice(numBags);
    }
}

Answer 2

希望你的考试不要来得太早，因为你有很多语法要复习。

我真的不喜欢直接给出家庭作业问题的答案，所以我会修复你目前拥有的东西，也许这会为你指明正确的方向。

Import.java.util.scanner;

public class discount {
  public static void main (String[] args){

    //Scanner input; Keep this as one line. It is good practice
    Scanner input = new Scanner(System.in);
    //Float bag;
   int bag;
    Float discount;
    Double cost = 3.75;

    //Input = new Scanner(System.ini);     combined with line above.
    System.out.println("Enter Numer of bag");
    bag = input.nextFloat();
    //If (bag ==>10&&<20) × .05  incorrect Java syntax

    //if(bag >= 10 && < 20) {
    if(bag >= 10 && bag < 20) {
     discount = 0.05;
    }
    else if(bag >= 20) {
      discount = 0.10;
    } 
    else {
      //discount = 0;
      discount = 0.0;
    }

    double finalPrice;
    finalPrice = (cost * bag) * (1 - discount);

    //System.out.println("You ordered " + bag + " bags of coffee.);
    System.out.println("You ordered " + bag + " bags of coffee.");
    System.out.println("Your dicount is " + discount + "%");
    System.out.println("Your total is: " + finalPrice);
  }
}

记得保持代码整洁，以免混淆自己。确保缩进代码。

考虑一下您为变量命名的内容，如果您想到更好的东西，请不要害怕重构它们。使用清晰且合乎逻辑的命名将减少您需要撰写的评论数量。

正如我之前提到的，研究你的语法。您的代码中有很多语法错误，这让我相信您可能是在记事本或命令行中编写代码？如果是这样，我建议使用 IDE，例如 IntelliJ、NetBeans 或 Eclipse。这些将强调您的语法错误并指出您可能不会立即注意到的错误。

Answer 3

if(bag >= 10 && < 20)

至

if(bag >= 10 && bag < 20)

初学者容易犯的错误！在学习基础知识时，我有点同意讲师关于编辑与 ide 的看法。您需要学习阅读编译器告诉您错误的内容。一旦你知道问题所在，我想你会同意，上面的语法错误消息很好地表明了问题所在。

简单折扣

Simple Discount

java

discount