⌛⌛ Movie data as a stream #2¶

Place your code into files named Movie.java and MovieAnalytics2.java in the round8/streams2 directory of your local repository. The test material is available in the corresponding directory in the remote materials repository.

This task concerns using the Java streams with tools from the Collectors class. The goal is to implement the MovieAnalytics2 class for producing grouped information about movie data by using the groupingBy function of the Collectors class. This task uses the Movie class from the previous task to represent movie data.

The MovieAnalytics2 class should have the following public features:

Constructor MovieAnalytics2() that initializes an empty movie database. A Movie list is a sufficient data structure also here.
Member function void populateWithData(String fileName) that reads movie data from the file specifed by the parameter. The function behaves as the corresponding function in previous task, but it must be implemented differently (see below).
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 movies. Directors with equally many movies are ordered by their names using the default order of the String objects. Each director is printed in the form "director: x movies", where x is the number of movies directed by that particular director. The output is printed in a single line that ends to a new line character.
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 default order of the String objects. Each genre is printed in the form "genre: average", where average is the average duration of movies in that genre, using two decimals of precision. The output is printed in a single line that ends to a new line character.
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 default order of the String objects. Each genre is printed in the form "genre: average", where average is the average rating score of movies in that genre, using two decimals of precision. The output is printed in a single line that ends to a new line character.

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. Since this restriction applies also to the reading of the file contents, implement also that part using a stream. Use the lines() function of the BufferedReader class to create 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 overly eager 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, for example .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, the movie data files input1.txt, input1.txt and input1.txt 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, for example, as javac *.java and run the tests as java MovieTest2 input1.txt 10, java MovieTest2 input2.txt 15 and java MovieTest2 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.