setDates和setTimes方法的前提条件是它们的参数都不为null。这是通过断言来检查的。 （这意味着如果不满足前提条件，程序将在断言时失败，并且将抛出AssertionError。）
这是我的代码：
public class Section
{
/**
* Default section number.
*/
private static final String DEFAULT_SECTION_NUMBER = "";
/**
* Constant for building Strings with newline characters within them.
*/
private static final String LINE_SEPARATOR = System.
getProperty("line.separator");
/**
* The maximum number of students permitted into a section.
*/
private static final int MAXIMUM_STUDENTS_PER_SECTION = 30;
/**
* Valid length for a sectionNumber string.
*/
private static final int SECTION_NUMBER_LENGTH = 3;
/**
* Shared variable for keeping count of the number of section objects in
* existence.
*/
private static int count = 0;
/**
* The date at which the section is finished.
*/
private Date endDate;
/**
* The end time for the meeting of the section.
*/
private Time2 endTime;
/**
* The list of students in the class. This declaration uses the Java 7 facility
* of not repeating the generic type if that type can be inferred by the
* compiler.
*/
private final List<Student> roster = new ArrayList<>();
/**
* The three-character designation of the section (called a
* “number”).
*/
private String sectionNumber = DEFAULT_SECTION_NUMBER;
/**
* The date on which the section starts to meet.
*/
private Date startDate;
/**
* The time of day at which the section meets.
*/
private Time2 startTime;
/**
* The course of which this is a section.
*/
private final Course thisCourse;
/**
* Constructor.
*
* @param course the course of which this is a section
* @param sectionNumber the section number (within the course) of this section
* @throws SectionException
*/
public Section(Course course, String sectionNumber) throws SectionException
{
/* Increment the collective count of all Section objects that have been
created. Do this first as the object already exists. */
++count;
this.thisCourse = course;
try
{
if( isValidSectionNumber(sectionNumber) )
this.sectionNumber = sectionNumber;
}
catch (Exception ex)
{
throw new SectionException("Error in constructor", ex);
}
}
/**
* Add a student to the course.
*
* @param student the student object to be added. If the course is full, the
* student is not added
*/
public void addStudent(Student student)
{
if( roster.size() != MAXIMUM_STUDENTS_PER_SECTION )
roster.add(student);
}
/**
* Get details about the current state of this section, including the course of
* which it is part, the dates it starts and ends, times, etc., and the current
* count of the enrollment.
*
* @return the section details
*/
public String getDetails()
{
return String.join(LINE_SEPARATOR,
"Section: " + this.toString(),
"Course: " + thisCourse.getDetails(),
"Dates: " + startDate + " to " + endDate,
"Times: " + startTime + " to " + endTime,
"Enrollment: " + roster.size());
}
/**
* Create a string that represents the information about the students in the
* course.
*
* @return a string that represents the information about the students in the
* course
*/
public String getRoster()
{
/* The following commented-out code is the obvious way to do this, using
String concatenation (and this is acceptable). However, the recommended
Java approach to this kind of operation is to use a StringJoiner (new
class in Java 8), as this uses less garbage collection resources. */
// String result = "";
// for( Student student : roster )
// {
// result += ( result.isEmpty() ? "" : LINE_SEPARATOR) + student;
// }
// return result;
StringJoiner stringJoiner = new StringJoiner(LINE_SEPARATOR);
for( Student student : roster )
stringJoiner.add(student.toString());
return stringJoiner.toString();
}
/**
* Get a count of the number of students registered (on the roster) for this course.
*
* @return a count of the number of students registered for this course
*/
public int getRosterCount()
{
return roster.size();
}
/**
* Get the section number for this course.
*
* @return the section number for this course
*/
public String getSectionNumber()
{
return sectionNumber;
}
/**
* Set the start and end dates for the section.
*
* @param startDate the start date
* @param endDate the end date
*/
public void setDates(Date startDate, Date endDate)
{
/* There is no requirement to validate these. */
this.startDate = startDate;
this.endDate = endDate;
}
/**
* Set the start time and the end time for the meetings of the section.
*
* @param startTime the start time for meetings of the section
* @param endTime the end time for the meetings of the section
*/
public void setTimes(Time2 startTime, Time2 endTime)
{
/* There is no requirement to validate these. */
this.startTime = startTime;
this.endTime = endTime;
}
/**
* Section number (prefixed)
*
* @return Section number (prefixed)
*/
@Override
public String toString()
{
return thisCourse.toString() + "-" + sectionNumber;
}
/**
* Finalization. Reduce the instance count by 1.
*
* @throws Throwable standard interface.
*/
@SuppressWarnings("FinalizeDeclaration")
@Override
protected void finalize() throws Throwable
{
/* Decrement the count of the collective total of all Section objects. */
--count;
super.finalize();
}
/**
* Get a count of how many total Section objects are currently in existence.
*
* @return a count of how many Section objects are currently in existence
*/
public static int getSectionCount()
{
return count;
}
/**
* Validate the sectionNumber string. It must be of the correct length.
*
* @param sectionNumber the sectionNumber string
* @return true if the string if valid, otherwise false
*/
private static boolean isValidSectionNumber(String sectionNumber)
{
return sectionNumber != null &&
sectionNumber.length() == SECTION_NUMBER_LENGTH;
}
}
我只是简单地断言＆＃39;在this.startDate = startDate之前;等等???我的书只有一个例子，它是为了确保一个值在0到10之间。
这是我的书中使用的例子：
public class AssertTest
{
public static void main(string[] args)
{
Scanner input = new Scanner(System.in);
System.out.print("Enter a number between 0 and 10: ");
int number = input.nextInt();
//assert that the value is >= 0 and <= 10
assert (number >= 0 && number <= 10) : "bad number: " + number;
System.out.printf("You entered %d%n", number);
}
}
所以我可以说
assert this.startDate = startDate
assert this.endDate = endDate
等等？
答案 0 :(得分：0)
首先，方法setTime和setDates是公开的，这表明它们可以在包之外使用。鉴于您无法控制参数 - 使用assert不会被视为最佳实践。当值可以在外部提供时（并且您无法控制它），您应该使用运行时异常，例如IllegalArgumentException：
if (startDate == null || endDate == null)
throw new IllegalArgumentException("Non-null arguments are required");
Assert的语法如下：
assert startDate != null;
assert endDate != null;
您还可以使用以下语法在断言失败时输出其他信息：
assert startDate != null : "startDate was set to null"
assert endDate != null : "endDate was set to null"