Question

我无法弄清楚我的程序的问题，非常感谢任何帮助！不幸的是，我是一名初学程序员...当我运行该程序时，它会正确地询问课程，学分和成绩的数量，但它忽略了输入的学分，只是给出了字母等级的正常值。最后它说＆＃34;你的GPA是0.0＆＃34;当显然是不正确的。再次感谢！

public class QualityPoints 
{
public static void main(String[] args) 
{
    // Needed variables

    String grade;
    int totalCredits = 0;
    int totalCreditsEarned = 0;
    int credits;
    int classes;
    double gpa;
    double number=0;

    String greeting = "This program will calculate your GPA.";
    JOptionPane.showMessageDialog(null, greeting, "GPA Calculator", 1);


    classes = Integer.parseInt(JOptionPane.showInputDialog(null, "Enter the number of classes you are taking"));



    //Loop that ends once the student has put information in on all his classes
    for(int count = 0; count < classes; count++)
    {   
        credits = Integer.parseInt(JOptionPane.showInputDialog(null, "How many credit was this class?:"));
        //reads the letter grade using the String Grade prompt



    // gathers input from user and assigns a string into JOptionPane
    grade = JOptionPane.showInputDialog(null, "Enter letter grade: ",
            "Quality Points Converter", JOptionPane.INFORMATION_MESSAGE);
    // calls separate method (computeQualityPoints) using parameter grade




        if (!grade.equalsIgnoreCase("a") && !grade.equalsIgnoreCase("a-")
                && !grade.equalsIgnoreCase("b+") && !grade.equalsIgnoreCase("b")
                && !grade.equalsIgnoreCase("b-") && !grade.equalsIgnoreCase("c+")
                && !grade.equalsIgnoreCase("c") && !grade.equalsIgnoreCase("c-")
                && !grade.equalsIgnoreCase("d+") && !grade.equalsIgnoreCase("d")
                && !grade.equalsIgnoreCase("d-") && !grade.equalsIgnoreCase("f")) {
            JOptionPane.showMessageDialog(null, "Invalid grade entered");
        } else {
            JOptionPane.showMessageDialog(null, "You received "
                    + computeQualityPoints(grade) + " quality points");
            computeQualityPoints(grade);

        }

        //algorithm for finding the GPA
        totalCredits += credits;
        totalCreditsEarned += (credits * number);
        }
        //for loop ends

        //GPA is calculated for all the students classes
        gpa = totalCreditsEarned / totalCredits;

    JOptionPane.showMessageDialog(null, "Your GPA is: " + gpa);

}

/**
 * Uses the letter grade given as the parameter to compute quality points
 * received, thus displaying quality points as the output
 * 
 * @param grade
 * @return JOptionPane message box with the number of quality points, given
 *         a valid letter grade.
 */

public static double computeQualityPoints(String grade) {

    /**
     * If/else statments providing the message attached to the output
     * corresponding to the grade
     */


    if (grade.equalsIgnoreCase("a")) {
        return 4.0;
    }
    if (grade.equalsIgnoreCase("a-")) {
        return 3.7;
    }
    if (grade.equalsIgnoreCase("b+")) {
        return 3.3;
    }
    if (grade.equalsIgnoreCase("b")) {
        return 3.0;
    }
    if (grade.equalsIgnoreCase("b-")) {
        return 2.7;
    }
    if (grade.equalsIgnoreCase("c+")) {
        return 2.3;
    }
    if (grade.equalsIgnoreCase("c")) {
        return 2.0;
    }
    if (grade.equalsIgnoreCase("c-")) {
        return 1.7;
    }
    if (grade.equalsIgnoreCase("d+")) {
        return 1.3;
    }
    if (grade.equalsIgnoreCase("d")) {
        return 1.0;
    }
    if (grade.equalsIgnoreCase("d-")) {
        return 0.7;
    }
    if (grade.equalsIgnoreCase("f")) {
        return 0.0;
    }
    return 0.0;
}
}

Answer 1

totalCreditsEarned += (credits * number);

number仍然是0.0，这意味着totalCreditsEarned和gpa也将保持0.0。

我怀疑

computeQualityPoints(grade);

你忽略了返回的值，应该是

number = computeQualityPoints(grade);

（至少我假设number应该包含的内容）

Answer 2

很明显，您忘记了computeQualityPoints的结果并将其存储在number变量中。因此，在向用户显示消息后，您应该更改以下行：

JOptionPane.showMessageDialog(null, "You received "
                    + computeQualityPoints(grade) + " quality points");
computeQualityPoints(grade);

到

JOptionPane.showMessageDialog(null, "You received "
                    + computeQualityPoints(grade) + " quality points");
number = computeQualityPoints(grade);

但是提高代码质量的其他一些提示：

您可以要求用户在循环中输入N'课程学分：

credits = Integer.parseInt(JOptionPane.showInputDialog(null, "How many credit was "+(count+1)+"'th class?"));

这为您的用户提供了更好的体验。

此外，您可以通过将其存储在地图结构（例如HashMap：

中）来更改检查程序中静态输入成绩的有效性的方式。

public class Snippet {

static HashMap<String,Float> GRADES = new HashMap<String, Float>(12);

static{
    GRADES.put("a", 4f);
    GRADES.put("a-", 3.7f);
    GRADES.put("b+", 3.3f);
    GRADES.put("b", 3f);
    GRADES.put("b-", 2.7f);
    GRADES.put("c+", 2.3f);
    GRADES.put("c", 2f);
    GRADES.put("c-", 1.7f);
    GRADES.put("d+", 1.3f);
    GRADES.put("d", 1f);
    GRADES.put("d-", 0.7f);
    GRADES.put("f", 0f);
}

public static void main(String[] args) {
    // Needed variables
    // ... you codes went here 
}

然后只需更改用户检查无效输入等级的方式：

if (!GRADES.containsKey(grade)) {
            JOptionPane.showMessageDialog(null, "Invalid grade entered");
        } else {
            JOptionPane.showMessageDialog(null, "You received "
                    + computeQualityPoints(grade) + " quality points");
            number = computeQualityPoints(grade);
        }

它可以帮助您计算number由于等级＆＃39;像这样：

public static float computeQualityPoints(String grade) {

        Float temp = GRADES.get(grade);
        if(temp == null){
            return 0;
        }

        return temp;
    }

您可能已经注意到我将computeQualityPoints的输出类型从double更改为float，因为您不需要为这么小的浮点值加倍。< / p>

如果您不想使用HashMap将if-else控件结构更改为switch-case，因为当您进行此类检查时，switch-case优先于if-else。

希望这会有所帮助。

Java GPA计算器问题

2 个答案: