具有"instanceof"的类型转换方法

Question

所以我在设置一些方法时遇到了一些问题，我盯着电脑屏幕看太久了。我对5种方法中的4种有困难。最后两个方法需要调用CompCiStudent类，因此使用"instanceof"，因为数组中并非所有Students都是CompCiStudents。这两种方法需要向Student数组中的Student添加CS语言，另一种方法是检查数组中有多少CompSciStudents知道特定语言。另外两种方法处理整个数组。第一种方法是只为某个位置的特定学生添加一个测试分数，当在数组中调用时，数组中的每个学生都会有一个特定的名字。最后一种方法是得到平均考试成绩。该方法是调用数组中Students和CompCiStudents的平均测试分数，并分别对每个分数进行平均，然后取这些平均值的平均值。看看类结构：

public class School {
    private Student[] theStudents;
    public School() {
        this.theStudents = new Student[] { null };// needs to start out as empty
    }
    /*
     * next two methods would allow a user to add or drop a student into the
     * student array for the school ??Also with Enroll student, should be able
     * to assign a class to the student, i.e. Calculas, history, etc??
     */
    public void enrollStudent(Student newStudent) {
        Student totalStudents[] = new Student[theStudents.length + 1];
        for (int i = 0; i < theStudents.length; i++) {
            totalStudents[i] = theStudents[i];
        }
        totalStudents[theStudents.length] = newStudent;
        theStudents = totalStudents;
    }
    public void dropStudent(Student dropStudent) {
        Student totalStudents[] = new Student[theStudents.length - 1];
        for (int i = 0; i > theStudents.length; i--) {
            totalStudents[i] = theStudents[i];
        }
        totalStudents[theStudents.length] = dropStudent;
        theStudents = totalStudents;
    }
    // add Test Score for a student
    public double addTestScore(String newStudent, double testScore) {
        testScores[posi] = testScore;
    }
    /*
     * count the number of students in a given class, not the school
     */
    public int countClassSize(String course) {
        // Need to access how the course names are stored for the school to
        // count this size.
        String courseName;
        if (this.courseName.equals(course)) {
            for (int i = 0; i < theStudents.length; i++) {
                int count = count + 1;
            }
        }
    }
    /*
     *  get average average score of the student array
     *  The student array is made up of Regular students and
     *  CompSciStudents. The average should take the average of
     *  both the average score for Students and average score of 
     *  CompSciStudents and return the average average.
     */
    public double averageAverageScore(String course) {
        double averageCourseScore;
        if(this.theStudents.equals(course)/2){
            return averageCourseScore;
        }
    }
    /*
     * add a programming language to only CS students at the school Will need to
     * use the instanceof for proper type casting
     */
    public String addProgrammingLanguage(String studentName, String programLanguage) {
        for (int i = 0; i ; i++);
        if (this.theStudents[i] instanceof CompSciStudent);
            CompSciStudent tempStudent = (CompSciStudent)this.theStudents[i];
                tempStudent.knowsLanguage(knowThisLanguage);
    }
    /*
     * Count the number of students in the school that know a certain
     * programming language, again will need to typecast properly
     */
    public int numberThatKnowLanguage(String programLanguage) {
        for();
                if(this.theStudents[i] instanceof CompSciStudent);
                CompSciStudent tempStudent = (CompSciStudent)this.theStudents[i];
                    tempStudent.learnedLanguage(knowThisLanguage);
    }

Answer 1

您面临的主要问题是应用程序的设计。我将提出一些设计改进建议，这些改进将有助于你解决问题。

1. 与其将theStudents[]声明为数组，不如将其设置为类似于List<Student> students的List。这将大大减少你在招生和退学时所付出的额外努力
2. 使用显式方法调用为学生添加主题不应该是理想的情况。科目应该与特定的学生有强烈的联系。为了遵守设计原则，学生对象的设计方式应为"学生有一个名称，has-aid，具有主题"。创建学生对象时要注意添加主题。因此，这就不需要添加额外的方法
3. 将学生分类为计算机科学专业的学生、电子专业的学生等应该在单独的班级中处理，比如我们称之为系。现在，为了简单起见，我们只考虑两个部门。一个是计算机科学，另一个是电子。"每个部门都有学生"。根据设计原则（有一个关系），你应该在你的系班级中创建一个List<Student> students（如第1点所述），最后你的学校班级将有一个List<Department> departments。这是一对多的关系
4. 在比较两个或多个Student对象时，不要忘记覆盖hashCode()和equals(Object obj)方法，因为它们是必要的

所以现在，你可以说"School有个系。每个Department都有有科目"。

现在你的类应该是这样的：

public class School {
    private List<Department> departments;
    /*
     * All your methods and constructors goes here.
     */
}
public class Department {
    private List<Student> students;
    /*
     * All your methods and constructors goes here.
     */
}
public class Student {
    private String name;
    private String id;
    private String courseStream;
    private List<String> subjects;
    /*
     * All your methods and constructors goes here.
     */
}

注意：我并不是说这是一个完美的设计。但对于你所解释的场景来说，这是相当微妙的。同样，代码设计可能因人而异。