在 Arrays.asList 中计算平均值时创建自定义异常

Question

我需要找到大学所有学生的平均成绩，并在 Arrays.asList 中找到平均成绩时创建自定义异常。如果 int warCraftGrade< 0 或 int warCraftGrade> 10，则应抛出异常。我有以下代码：

public class Student {
String name;
public final int warCraftGrade;

public Student(String name, int warCraftGrade) {
    this.name = name;
    this.warCraftGrade = warCraftGrade;
}
public String getName() {
    return name;
}
public int getWarCraftGrade() {
    return warCraftGrade;
}

我有学生名单：

static List<Student> students = Arrays.asList(
    new Student("Geoffrey Baratheon", 8),
    new Student("Barristan Selmy", 6) //and so on
);

以及取平均值的方法：

double warCraftAverageGrade = students.stream()
                .mapToDouble(Student::getWarCraftGrade)
                .average()
                .getAsDouble();

我创建了特殊例外 class:

public class GradeException extends Exception{
public GradeException() {
}
public GradeException(String message) {
    super(message);
}
public GradeException(String message, Throwable cause) {
    super(message, cause);
}

和class定义异常方法：

public class StudentActions {
public static void range (Student student) throws GradeException {
    if (student.warCraftGrade < 0 || student.warCraftGrade > 10) {
        throw new GradeException("Wrong grade");
    }
}

} 当我尝试使用 StudentActions.range() 方法时出现问题：

public static void main(String[] args) {
    try {
        StudentActions.range();
        double warCraftAverageGrade = students.stream()
                .mapToDouble(Student::getWarCraftGrade)
                .average()
                .getAsDouble();
        System.out.println("Average grade in WarCraft for the entire university = " + warCraftAverageGrade);
    } catch (GradeException e) {
        System.out.println("Grade is out of range (0-10)");
    }

在这种情况下形成自定义异常的正确解决方案是什么？例如，如果成绩为负数，则正确的代码必须抛出 GradeException：

//new Student("Jorah Mormont", -8)

提前致谢！

Answer 1

最好将异常移动到构造函数中，而不是每次获取平均值时都必须捕获异常。简单地让你不能构造一个无效的对象。在您的特定情况下，抛出已检查的异常（不扩展 RuntimeException 并附加到 throws 子句，迫使调用者处理它的异常）没有意义。

This answer 建议何时适合使用检查异常（强调我的）：

I also think that throwing checked exceptions can be OK¹, assuming that the checked exception is 1) declared, 2) specific to the problem you are reporting, and 3) it is reasonable to expect the caller to deal with a checked exception for this².

^{2 - For example, the existing FileInputStream constructors will throw FileNotFoundException if you try to open a file that does not exist. Assuming that it is reasonable for FileNotFoundException to be a checked exception³, then the constructor is the most appropriate place for that exception to be thrown. If we threw the FileNotFoundException the first time that (say) a read or write call was made, that is liable to make application logic more complicated.}

此外，我建议将实际成绩范围逻辑移动到一个方法中，而不是强制调用者每次都这样做。

最后一件事：我会让你的方法成为非静态的，因为你正在处理一个实例。在 Java（我不知道你来自什么语言）中，this，当前实例在所有非静态方法中都可用，并且优于将实例传递给静态方法。

看看这些问题：

When to throw an exception?
Is it good practice to make the constructor throw an exception?

在 Arrays.asList 中计算平均值时创建自定义异常

Creating Custom Exception while calculating the average in the Arrays.asList

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