在Java中创建列表的2D动态数组

Question

I am trying to implement a 2D dynamic array of lists in Java to store a list of Course objects for a given Student and Week object.

Something along the line, List<List<List<Course>>> listOfCoursesInWeekForStudent = new ArrayList<List<List<Course>>>();

Could you please show me how to create such a structure, and perform simple operations on it including add and get.

Thank you

Answer 1

Could you please show me how to create such a structure, and perform simple operations on it including add and get .

The data-structure is List<List<List<Course>>> , so it is a List containing elements of type List<List<Course>> .

You create it exactly like you've shown, using:

List<List<List<Course>>> listOfListOfListOfCourses = new ArrayList<>();

Adding and getting elements works as usual, just have in mind that the elements are of type List<List<Course>> :

List<List<Course>> element = ...
// Add element
listOfListOfListOfCourses.add(element);
// Get index of element
int index = listOfListOfListOfCourses.get(element);

However, as you might have noticed, the data-structure is complicated . I'm sure in your exact context there is a more appropriate data-structure. Unfortunately you didn't provide additional information about your specific task. You may provide it and leave a comment.

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Example

Let's try to create a simple example in order to see how such a data-structure could be of use. Therefore

List<Course>             // All courses of one semester
List<List<Course>>       // All semesters of one university
List<List<List<Course>>> // All universities of one country

In this specific example you easily see that it would be of great help if you create some small wrapper classes like

public class Semester {
    private List<Course> mCourses;

    public Semester(List<Course> courses) {
        this.mCourses = courses;
    }

    public List<Course> getCourses() {
        return this.mCourses;
    }
}

public class University {
    private List<Semester> mSemesters;

    public University(List<Semester> semesters) {
        this.mSemesters = semesters;
    }

    public List<Semester> getSemesters() {
        return this.mSemesters;
    }
}

Using this your data-structure breaks down to

List<University> // Universities of one country

Far more easy to read and understand.