简化GPA计算器

Question

我只学习了两个星期的Java，并且刚刚完成了我的第一个程序。我有种感觉，我增加了不必要的东西，但不确定。我希望有人看看它，并让我知道是否有方法来简化或接近代码。基本上，我只是想创建一个简单的GPA计算器。

import java.util.Scanner;

class GpaCalculator {

    public static void main(String[] args) {
        Scanner myScanner = new Scanner(System.in);
        char c1;
        double gpa;
        double g1, g2, g3, g4, g5, g6;

        g1 = 0;
        g2 = 0;
        g3 = 0;
        g4 = 0;
        g5 = 0;
        g6 = 0;

        System.out.println("What is your grade for class 1?");
        c1 = myScanner.findWithinHorizon(".", 0).charAt(0);
        if (c1 == 'a' || c1 == 'A') {
            g1 = 4;
        }
        if (c1 == 'b' || c1 == 'B') {
            g1 = 3;
        }
        if (c1 == 'c' || c1 == 'C') {
            g1 = 2;
        }
        if (c1 == 'd' || c1 == 'D') {
            g1 = 1;
        }
        if (c1 == 'f' || c1 == 'F') {
            g1 = 0;
        }
        System.out.println("What is your grade for class 2?");
        c1 = myScanner.findWithinHorizon(".", 0).charAt(0);
        if (c1 == 'a' || c1 == 'A') {
            g2 = 4;
        }
        if (c1 == 'b' || c1 == 'B') {
            g2 = 3;
        }
        if (c1 == 'c' || c1 == 'C') {
            g2 = 2;
        }
        if (c1 == 'd' || c1 == 'D') {
            g2 = 1;
        }
        if (c1 == 'f' || c1 == 'F') {
            g2 = 0;
        }
        System.out.println("What is your grade for class 3?");
        c1 = myScanner.findWithinHorizon(".", 0).charAt(0);
        if (c1 == 'a' || c1 == 'A') {
            g3 = 4;
        }
        if (c1 == 'b' || c1 == 'B') {
            g3 = 3;
        }
        if (c1 == 'c' || c1 == 'C') {
            g3 = 2;
        }
        if (c1 == 'd' || c1 == 'D') {
            g3 = 1;
        }
        if (c1 == 'f' || c1 == 'F') {
            g3 = 0;
        }
        System.out.println("What is your grade for class 4?");
        c1 = myScanner.findWithinHorizon(".", 0).charAt(0);
        if (c1 == 'a' || c1 == 'A') {
            g4 = 4;
        }
        if (c1 == 'b' || c1 == 'B') {
            g4 = 3;
        }
        if (c1 == 'c' || c1 == 'C') {
            g4 = 2;
        }
        if (c1 == 'd' || c1 == 'D') {
            g4 = 1;
        }
        if (c1 == 'f' || c1 == 'F') {
            g4 = 0;
        }
        System.out.println("What is your grade for class 5?");
        c1 = myScanner.findWithinHorizon(".", 0).charAt(0);
        if (c1 == 'a' || c1 == 'A') {
            g5 = 4;
        }
        if (c1 == 'b' || c1 == 'B') {
            g5 = 3;
        }
        if (c1 == 'c' || c1 == 'C') {
            g5 = 2;
        }
        if (c1 == 'd' || c1 == 'D') {
            g5 = 1;
        }
        if (c1 == 'f' || c1 == 'F') {
            g5 = 0;
        }
        System.out.println("What is your grade for class 6?");
        c1 = myScanner.findWithinHorizon(".", 0).charAt(0);
        if (c1 == 'a' || c1 == 'A') {
            g6 = 4;
        }
        if (c1 == 'b' || c1 == 'B') {
            g6 = 3;
        }
        if (c1 == 'c' || c1 == 'C') {
            g6 = 2;
        }
        if (c1 == 'd' || c1 == 'D') {
            g6 = 1;
        }
        if (c1 == 'f' || c1 == 'F') {
            g6 = 0;
        }

        gpa = (g1 + g2 + g3 + g4 + g5 + g6) / 6;

        System.out.println("Your GPA is " + gpa + ". ");

        if (gpa > 3.00) {
            System.out.println("Gret job, you're on your way to success.");
        } else if (gpa > 2.00) {
            System.out.println("You did OK, but better than average.");
        } else {
            System.out.println("You didn't do too well. You should look into getting a tutor.");
        }
    }
}

Answer 1

首先，Grade和Class (避免与java.lang.Class混淆的GradedClass)作为枚举都是有意义的。

enum Grade {
    A(4),B(3),C(2),D(1),F(0);

    private final int value;

    Grade(int value) {
        this.value = value;
    }

    int getValue() {
        return value;
    }
}

enum GradedClass {
    ONE, TWO, THREE, FOUR, FIVE, SIX;

    @Override
    public String toString() {
        return "class " + (ordinal() + 1);
    }
}

这将允许一个更简单的计算循环：

    public double calculateGpa() {
        return calculateTotal() / GradedClass.values().length;
    }

    private double calculateTotal() {
        double total = 0d;
        for (GradedClass gradedClass : GradedClass.values()) {
            Grade grade = userInterface.askGradeFor(gradedClass);
            total += grade.getValue();
        }
        return total;
    }

请注意，为了将计算与UI代码分开，我已经将扫描仪隐藏在UserInterface接口后面。

它由ConsoleUI类实现：

class ConsoleUI implements UserInterface {
    Scanner myScanner = new Scanner(System.in);

    @Override
    public Grade askGradeFor(GradedClass gradedClass) {
        System.out.println(MessageFormat.format("What is your grade for {0}?", gradedClass));
        String input = myScanner.findWithinHorizon(".", 0);
        return Grade.valueOf(input.toUpperCase());
    }

    @Override
    public void presentGpa(double gpa) {
        if (gpa > 3d) {
            System.out.println("Great job, you're on your way to success.");
        } else if (gpa > 2d) {
            System.out.println("You did OK, but better than average.");
        } else {
            System.out.println("You didn't do too well. You should look into getting a tutor.");
        }
    }

}

主要的课程只是把所有的东西联系在一起：

public class Main {

    public static void main(String[] args) {
        UserInterface ui = new ConsoleUI();
        GpaCalculator gpaCalculator = new GpaCalculator(ui);

        double gpa = gpaCalculator.calculateGpa();
        ui.presentGpa(gpa);
    }

}

Answer 2

我将对您的代码进行如下改进：

• 看看您的代码，您会注意到同一段代码的重复(打印问题=>扫描输入=>分析输入)，这意味着您可以为此编写一个方法。
• 如果你想要多一个等级，你必须创建一个新的变量，等等。我会把分数存储在数组中。
• 实际上，我甚至不确定我是否会把它们存储在一个数组中:只要把分数和起来，然后除以年级数
• 小写用户输入，所以您不必测试小写和大写。
• 使用if ... else if而不是几个if
• 在您的示例中，使用0初始化级别，并在用户键入f时存储0。没有必要处理这个案子。
• 你不处理E级吗？

代码看起来应该是这样的：

import java.util.Scanner;

public class GpaCalculator {
    private final static Scanner MY_SCANNER = new Scanner(System.in);
    private final static int NUMBER_OF_GRADES = 6;

    public static void main(final String[] args) {
        int sum = 0;
        for (int i = 0; i < NUMBER_OF_GRADES; i++) {
            sum += askForGrade(i);
        }
        final double gpa = (double) sum / NUMBER_OF_GRADES;

        System.out.println("Your GPA is " + gpa + ". ");

        if (gpa > 3.00) {
            System.out.println("Gret job, you're on your way to success.");
        } else if (gpa > 2.00) {
            System.out.println("You did OK, but better than average.");
        } else {
            System.out.println("You didn't do too well. You should look into getting a tutor.");
        }
    }

    private static int askForGrade(final int index) {
        System.out.println("What is your grade for class " + (index + 1) + "?");
        char c1 = MY_SCANNER.findWithinHorizon(".", 0).charAt(0);
        c1 = Character.toLowerCase(c1);

        switch(c1){
            case 'a':
                return 4;
            case 'b':
                return 3;
            case 'c':
                return 2;
            case 'd':
                return 1;
            default:
                return 0;
        }
    }
}

最后，您可以改进提示符，只接受真正的分数(在您的代码中，在我的代码中，用户可以提供任何字符)。

Answer 3

• 首先，尝试考虑GpaCalculator的所有逻辑和行为，并在类中将它们分开。
• 就像bowmore建议的那样，您可以使用enum，这对于您的代码是灵活的。

这是我对你的代码的版本。

• 还试着考虑可以从代码(如例外情况 )中引发的IllegalGradeException。

GradeCalculator类

    package com.se.cr;

    import java.util.Scanner;

    public class GradeCalculator {

        private final int NUMBER_OF_CLASSES;
        private Scanner myScanner = new Scanner(System.in);

        // Default constructor
        public GradeCalculator(){
            this(6); // By default number of classes are 6
        }

        // Customize constructor
        public GradeCalculator(int NUMBER_OF_CLASSES){
            this.NUMBER_OF_CLASSES = NUMBER_OF_CLASSES;
        }

        public double calculateGPA(){
            final double GPA = this.calculateSum() / NUMBER_OF_CLASSES;
            return GPA;
        }

        protected double calculateSum(){
            double sum = 0.0;
            for(int i = 1; i <= NUMBER_OF_CLASSES; i++){
                sum += this.gradeValue(i);
            }
            return sum;
        }

        /**
         * 
         * @param classNumber 
         * @return grade of that particular <code> classNumber </code>
         */
        protected double gradeValue(int classNumber){
            System.out.print("What is your grade for class " + classNumber + " ? ");
            char gradeChar = myScanner.next().toLowerCase().charAt(0);

                while(gradeChar < 'a' || gradeChar > 'f'){
                System.out.println("Wrong choice"); // raise an exception here and handle it
                System.out.print("What is your grade for class " + classNumber + " ? ");
                gradeChar = myScanner.next().toLowerCase().charAt(0);
            }
            return this.toGradeValue(gradeChar);
        }

        /**
         * 
         * @param grade
         * @return numeric representation of <code> grade </code>
         */
        public double toGradeValue(char grade){
            double gradeValue = 0.0;
            switch (grade) {
                case 'a': gradeValue = 5.0; break;
                case 'b': gradeValue = 4.0; break;
                case 'c': gradeValue = 3.0; break;
                case 'd': gradeValue = 2.0; break;
                case 'e': gradeValue = 1.0; break;
                case 'f': gradeValue = 0.0; break;
            }
            return gradeValue;
        }
    }

教师班您还可以使它成为一个单独的类，而不是像bowmore所建议的那样，使它成为一个主类.。

    package com.se.cr;

    public class Teacher {

        public static void main(String[] args) {
            GradeCalculator calculator = new GradeCalculator();
            final double GPA = calculator.calculateGPA();

            Teacher teacher = new Teacher();
            teacher.takeDecision(GPA); 
        }

        /**
         * Teacher will take decision on the basis of <code> GPA </code> 
         * @param GPA 
         */
        protected void takeDecision(final double GPA){
            System.out.println("Your GPA is " + GPA);
            if (GPA > 3.00) {
                System.out.println("Gret job, you're on your way to success.");
            } else if (GPA > 2.00) {
                System.out.println("You did OK, but better than average.");
            } else {
                System.out.println("You didn't do too well. You should look into getting a tutor.");
            }
        }
    }