Question

方法markStudent（...）和getUnitMark（...）中的前提条件代码使用了该类的其他方法：isEnrolled（...）和hasCompletedAssessments（...）。

import java.util.ArrayList; 
import java.util.HashMap;
public class Unit {
    private String code;
    private String name;
    private HashMap<Integer, Student> enrolledStudents = new HashMap<Integer, Student>(); 
    private AssessmentScheme assessmentScheme = null;
    private HashMap<Assessment, HashMap<Student, Mark> > Marks

    public Unit(String newCode, String newName) { code = newCode;
             name = newName;
       }
    public void enrolStudent(Student newStudent) {
             enrolledStudents.put(newStudent.getPersonID(), newStudent);
       }
    public void unenrolStudent(Student student) {
             enrolledStudents.remove(student.getPersonID());
       }

    public boolean isEnrolled(Student student) {
            return enrolledStudents.containsKey(student.getPersonID()); }
    public ArrayList<Student> getEnrolledStudents() {
            ArrayList<Student> students = new ArrayList<Student (enrolledStudents.values());
            return students; }

    public boolean hasCompletedAssessments(Student student) { boolean hasCompleted = true;
            for (Assessment a : assessmentScheme.getAssessments()) {       hasCompleted &= Marks.get(a).containsKey(student);
} 
    return hasCompleted; }

    public void markStudent(Assessment assessment, Student student, int score, String comment) throws Exception {
        /* Start Preconditions */
        // Precondition: studentEnrolledInUnit
        if (! isEnrolled(student)) {
             } throw new Exception("Precondition violated: studentEnrolledInUnit");
        // Precondition: scoreInValidRange
        if ((score < 0 || (score > assessment.getWeight()) } 
            throw new Exception("Precondition violated: scoreInValidRange"); /* End Preconditions */
        Mark mark = new Mark(assessment, student, score, comment);
               Marks.get(assessment).put(student, mark);
}

问题是，前提条件代码中使用的方法（例如isEnrolled（...）和hasCompletedAssessments（...））是公开的还是私有的？

根据我对合同设计的理解，客户应检查其论点是否符合前提条件。这意味着在前提条件代码中使用的方法应该是公共的，以便客户端类可以进行检查。但是，在markStudent方法中，可以清楚地看到该方法正在检查其自身的前提条件。有人可以帮忙吗？

Answer 1

公开这些方法没有任何危害。这样一来，客户就可以确保其通话合法。如果客户知道自己的通话合法，则不必这样做。

方法实现也可以通过调用公共方法自己进行检查。

前提方法应该是公开的还是私有的？

1 个答案: