⌛⌛ Movie data vs stream #2¶

Place your code into files named Movie.java and MovieAnalytics2.java in the directory Round7/streams2. Also remember to pull task material from student_template_project.

This task concerns using java streams with tools from the Collectors class. The goal is to implement a class MovieAnalytics2 that produces grouped information about movie data by using the groupingBy function of the Collectors class. This task uses the same simple class Movie for representing movie data as the previous task.

The class MovieAnalytics2 should have the following public features:

Constructor MovieAnalytics2() that initializes an empty movie database. E.g a simple Movie list is again fine.

Member function void populateWithData(String fileName) that reads movie data from the file spedicifed by the parameter.

The file is expected to contain lines of form “title;releaseYear;duration;genre;score;director”.

Member function void printCountByDirector(int n) that prints out the n directors that have directed the most movies, in descending order of the number of directed movies. Directors with equally many movies are ordered by their names (using the natural String order). Each director is output in the form “director: x movies”, where x is the number of movies directed by that particular director.
Member function void printAverageDurationByGenre() that prints out all movie genres of the database in ascending order of the average duration of movies in that genre. Movies in the same genre are ordered by title (using the natural String order). Each genre is output in the form “genre: average”, where average is the average duration of movies in that genre, using two decimals of precision.
Member function void printAverageScoreByGenre() that prints out all movie genres of the database in descending order of the average rating scores of movies in that genre. Genres with the same average rating are ordered by genre name (using the natural String order). Each genre is output in the form “genre: average”, where average is the average rating score of movies in that genre, using two decimals of precision.

You should use streams in this task. To this end, the grading system seeks to enforce a rule that the file MovieAnalytics2.java cannot contain any for- or while-loops. This restriction applies also to reading the file contents, so implement also that part using a stream (ie. use the BufferedReader member function lines() that creates a stream that reads input line by line).

A note about the grader’s so-called “loop detection”

The grader uses a very crude method for detecting loops: it checks that the source code does not contain the keywords “for” or “while”. The detection is stupid in the sense that it matches also words like “form” that begin with the forbidden word “for”. These keywords are allowed, however, if they are directly preced by a dot so that e.g. .forEach and .format are allowed. Therefore do not use variable or function names (or even words in comments) that begin with “for” or “while”.

Testing¶

You may test your implementation by using the test program given in the file MovieTest2.java and the example output given in the files output1.txt, output2.txt and output3.txt. Place these files to the same directory with your code, compile the test program e.g. as javac *.java, and run the tests as java MovieTest input1.txt 10, java MovieTest input2.txt 15 and java MovieTest input3.txt 20. The expected outputs of these tests are given in the files output1.txt, output2.txt and output3.txt.

A+ presents the exercise submission form here.