Question

刚刚开始使用这个非常简单的GPA计算器，想知道如何使用循环来避免大量的switch语句？我是Java的新手，只是寻求一些建议，非常感谢任何其他改进程序的方法。先谢谢你，伙计们！

package helloPackage;
import javax.swing.JOptionPane;

public class GradePointAverage {

public static void main(String[] args) {
    System.out.println("Welcome to the GPA calculator! Please enter your GPA into the popup window to find your GPA.");

    String firstClassInput = JOptionPane.showInputDialog(null,"Please enter your grade for your first class: (A+, A, A-, B+, etc.)");
    String firstClass = firstClassInput.toUpperCase();
    String secondClassInput = JOptionPane.showInputDialog(null,"Please enter your grade for your second class: (A+, A, A-, B+, etc.)");
    String secondClass = secondClassInput.toUpperCase();
    String thirdClassInput = JOptionPane.showInputDialog(null,"Please enter your grade for your third class: (A+, A, A-, B+, etc.)");
    String thirdClass = thirdClassInput.toUpperCase();
    String fourthClassInput = JOptionPane.showInputDialog(null,"Please enter your grade for your fourth class: (A+, A, A-, B+, etc.)");
    String fourthClass = fourthClassInput.toUpperCase();
    String fifthClassInput = JOptionPane.showInputDialog(null,"Please enter your grade for your fifth class: (A+, A, A-, B+, etc.)");
    String fifthClass = fifthClassInput.toUpperCase();

    double firstGrade = 0.0;
    double secondGrade = 0.0;
    double thirdGrade = 0.0;
    double fourthGrade = 0.0;
    double fifthGrade = 0.0;

    switch (firstClass){
    case "A+": firstGrade = 4.33;
        break;
    case "A": firstGrade = 4.00;
        break;
    case "A-": firstGrade = 3.67;
        break;
    case "B+": firstGrade = 3.33;
        break;
    case "B": firstGrade = 3.00;
        break;
    case "B-": firstGrade = 2.67;
        break;
    case "C+": firstGrade = 2.33;
        break;
    case "C": firstGrade = 2.00;
        break;
    case "C-": firstGrade = 1.67;
        break;
    case "D+": firstGrade = 1.33;
        break;
    case "D": firstGrade = 1.00;
        break;
    case "D-": firstGrade = .67;
        break;
    case "F": firstGrade = 0.0;
        break;
    }

    switch (secondClass){
    case "A+": secondGrade = 4.33;
        break;
    case "A": secondGrade = 4.00;
        break;
    case "A-": secondGrade = 3.67;
        break;
    case "B+": secondGrade = 3.33;
        break;
    case "B": secondGrade = 3.00;
        break;
    case "B-": secondGrade = 2.67;
        break;
    case "C+": secondGrade = 2.33;
        break;
    case "C": secondGrade = 2.00;
        break;
    case "C-": secondGrade = 1.67;
        break;
    case "D+": secondGrade = 1.33;
        break;
    case "D": secondGrade = 1.00;
        break;
    case "D-": secondGrade = .67;
        break;
    case "F": secondGrade = 0.0;
        break;
    }
    switch (thirdClass){
    case "A+": thirdGrade = 4.33;
        break;
    case "A": thirdGrade = 4.00;
        break;
    case "A-": thirdGrade = 3.67;
        break;
    case "B+": thirdGrade = 3.33;
        break;
    case "B": thirdGrade = 3.00;
        break;
    case "B-": thirdGrade = 2.67;
        break;
    case "C+": thirdGrade = 2.33;
        break;
    case "C": thirdGrade = 2.00;
        break;
    case "C-": thirdGrade = 1.67;
        break;
    case "D+": thirdGrade = 1.33;
        break;
    case "D": thirdGrade = 1.00;
        break;
    case "D-": thirdGrade = .67;
        break;
    case "F": thirdGrade = 0.0;
        break;
    }
    switch (fourthClass){
    case "A+": fourthGrade = 4.33;
        break;
    case "A": fourthGrade = 4.00;
        break;
    case "A-": fourthGrade = 3.67;
        break;
    case "B+": fourthGrade = 3.33;
        break;
    case "B": fourthGrade = 3.00;
        break;
    case "B-": fourthGrade = 2.67;
        break;
    case "C+": fourthGrade = 2.33;
        break;
    case "C": fourthGrade = 2.00;
        break;
    case "C-": fourthGrade = 1.67;
        break;
    case "D+": fourthGrade = 1.33;
        break;
    case "D": fourthGrade = 1.00;
        break;
    case "D-": fourthGrade = .67;
        break;
    case "F": fourthGrade = 0.0;
        break;
    }
    switch (fifthClass){
    case "A+": fifthGrade = 4.33;
        break;
    case "A": fifthGrade = 4.00;
        break;
    case "A-": fifthGrade = 3.67;
        break;
    case "B+": fifthGrade = 3.33;
        break;
    case "B": fifthGrade = 3.00;
        break;
    case "B-": fifthGrade = 2.67;
        break;
    case "C+": fifthGrade = 2.33;
        break;
    case "C": fifthGrade = 2.00;
        break;
    case "C-": fifthGrade = 1.67;
        break;
    case "D+": fifthGrade = 1.33;
        break;
    case "D": fifthGrade = 1.00;
        break;
    case "D-": fifthGrade = .67;
        break;
    case "F": fifthGrade = 0.0;
        break;
    }

    double total = firstGrade + secondGrade + thirdGrade + fourthGrade + fifthGrade;  
    double GPA = total / 5;
    System.out.println("Your GPA is: " + GPA);
}

}

Answer 1

使用double getGrade(String)之类的方法，如下所示

double firstGrade = getGrade(firstClass);
double secondGrade = getGrade(secondClass);
double thirdGrade = getGrade(thirdClass);
double fourthGrade = getGrade(fourthClass);
double fifthGrade = getGrade(fifthClass);

// Use your switch statement.... no break(s) because we return.
public static double getGrade(String grade) {
  switch (grade){
  case "A+": return 4.33;
  case "A": return 4.00;
  case "A-": return 3.67;
  case "B+": return 3.33;
  case "B": return 3.00;
  case "B-": return 2.67;
  case "C+": return 2.33;
  case "C": return 2.00;
  case "C-": return 1.67;
  case "D+": return 1.33;
  case "D": return 1.00;
  case "D-": return .67;
  }
  // F
  return 0.0;
}

Answer 2

您可以轻松创建一个Enum来表示这些成绩，并将成绩的值作为字段添加到枚举中。

Answer 3

不使用firstGrade，secondgrade等，而是使用数组或列表：

double[] grades = new double[5]; // firstGrade will be grades[0], and so on.

对于字母成绩，我建议使用枚举，使用valueOf()方法。

Answer 4

此方法删除所有开关，并仅使用两个if语句：

public static double getGrade(String grade) {
  double retVal = 0.0;
  char letter = grade.getCharAt(0); //Get the letter grade

  //Compute the base grade--some of these casts may not be needed 
  //(I'm not figuring it out right now)
  retVal = Math.max((int)'A' - (int)letter + 4, 0.0);

  if (grade.length() == 1) return retVal;

  //Alter the grade based on the postfix
  char pm = grade.getCharAt(1); //Get the plus/minus

  if (pm == '+') retVal += 0.33;
  else           retVal -= 0.33;

  return retVal;
}

然后，使用“Chthonic Project”答案中提到的数组方法。

Answer 5

您只需要一个大的switch语句。

而不是拥有firstClass / firstGrade / secondClass / secondGrade，只需要两个数组，class []和grade []。然后你可以做类似的事情：

for(int i = 0; i < 5; i++){
    switch(class[i]){
         case "A+" : grade[i] = 4.33;
    }
 }

Answer 6

如果将一些类似的任务封装到单独的方法中，它应该使您的代码更清晰一些。试试这个。希望这有帮助

public static void main(String[] args) {
    System.out
            .println("Welcome to the GPA calculator! Please enter your GPA into the popup window to find your GPA.");

    String firstClassInput = JOptionPane
            .showInputDialog(null,
                    "Please enter your grade for your first class: (A+, A, A-, B+, etc.)");
    String firstClass = firstClassInput.toUpperCase();
    String secondClassInput = JOptionPane
            .showInputDialog(null,
                    "Please enter your grade for your second class: (A+, A, A-, B+, etc.)");
    String secondClass = secondClassInput.toUpperCase();
    String thirdClassInput = JOptionPane
            .showInputDialog(null,
                    "Please enter your grade for your third class: (A+, A, A-, B+, etc.)");
    String thirdClass = thirdClassInput.toUpperCase();
    String fourthClassInput = JOptionPane
            .showInputDialog(null,
                    "Please enter your grade for your fourth class: (A+, A, A-, B+, etc.)");
    String fourthClass = fourthClassInput.toUpperCase();
    String fifthClassInput = JOptionPane
            .showInputDialog(null,
                    "Please enter your grade for your fifth class: (A+, A, A-, B+, etc.)");
    String fifthClass = fifthClassInput.toUpperCase();

    List<String> listOfGrades = new ArrayList<String>();
    listOfGrades.add(firstClass);
    listOfGrades.add(secondClass);
    listOfGrades.add(thirdClass);
    listOfGrades.add(fourthClass);
    listOfGrades.add(fifthClass);

    double GPA = getGPA( listOfGrades );
    System.out.println("Your GPA is: " + GPA);
}


/**
 * Used to calculate GPA from list of supplied grades
 * 
 * @param listOfGrades as list of grades to compute GPA
 * @return GPA as double
 */
public static double getGPA(List<String> listOfGrades){
    double total = 0.0;
    double GPA = 0.0;

    for(String aGrade: listOfGrades){
         total += getGrade( aGrade );

    }
    GPA = total / listOfGrades.size();
    System.out.println("Total "+total+" amount of grades: "+listOfGrades.size());
    return GPA;
}

/**
 * Get value of grade as a double type
 * 
 * @param stringGrade Grade
 * @return value of grade as 
 */
public static double getGrade(String stringGrade ){

    double grade = 0.0;
    switch (stringGrade) {
    case "A+":
        grade = 4.33;
        break;
    case "A":
        grade = 4.00;
        break;
    case "A-":
        grade = 3.67;
        break;
    case "B+":
        grade = 3.33;
        break;
    case "B":
        grade = 3.00;
        break;
    case "B-":
        grade = 2.67;
        break;
    case "C+":
        grade = 2.33;
        break;
    case "C":
        grade = 2.00;
        break;
    case "C-":
        grade = 1.67;
        break;
    case "D+":
        grade = 1.33;
        break;
    case "D":
        grade = 1.00;
        break;
    case "D-":
        grade = .67;
        break;
    case "F":
        grade = 0.0;
        break;
    }
    System.out.println("stringGrade: "+stringGrade+"="+grade);
    return grade;
}

Answer 7

我建议使用枚举或地图，主要是因为有最人性化的替代品，它也为您提供了一个很好的机会来解耦数据UI /逻辑层。

示例枚举：

public enum Grades {
    APLUS("A+", 4.33),
    A("A",4.00);

    private String label;
    private double value;
    private Grades(String label,double value){
        this.label = label;
        this.value = value;
    }

    public double getValue() {
        return value;
    }

    public static Grades getByLabel(String label){
        for(Grades grades : values()){
            if(grades.label.equals(label)){
                return grades;
            }
        }
        throw new IllegalArgumentException("Incorrect Label");
    }

}

稍后在您的代码Grades.getByLabel(firstGrade).getValue();中使用如果您计划添加连接到每个等级的任何额外数据，则枚举非常好。一些其他类型的测量或类似，那么就不需要几个数组，列表或类似的。

示例地图（在单独的类中）：

public class GradeValues {
private static Map<String,Double> gradeValues = new HashMap<String, Double>();
static{
    gradeValues.put("A+", 4.33);
    gradeValues.put("A", 4.00);
}

public static double getGradeValue(String grade){
    return gradeValues.get(grade);
}

}

稍后在您的代码中使用：

GradeValues.getGradeValue(firstGrade);

这些转换语句有哪些替代方案？

7 个答案: