CS46B Homework 3: Basic Java Classes

Getting started

Create a new workspace directory, or use an existing one. Create a Java project called hw3proj in the workspace. Create a package called movies in the project. All classes and interfaces that you create should go in the movies package.

Class movie Create a public class Movie with private instance variables String title and int year. The class should declare that it implements the Comparable interface, and should provide the following: A constructor that takes 2 arguments: a String and an int (in that order) for initializing title and year. A method that satisfies the Comparable interface. Movies should be compared first by title and then by year. Methods getTitle() and getYear() that do the right thing. An equals() method that is compatible with the method that satisfies the Comparable interface. A toString() method that returns Movie followed by 1 space followed by the title followed by 1 space followed by open-parenthesis followed by the year followed by close-parenthesis. Example: Movie The Maltese Falcon (1941) A public static method getTestMovies(), which returns an array of 10 unique Movie instances. They dont have to be real movies its ok to make them up. The 0th and 1st array elements must be 2 movies with the same title but from different years (e.g. The Thomas Crown Affair 1968 and The Thomas Crown Affair 1999, or True Grit 1969 and True Grit 2010). The 2nd and 3rd elements (counting from 0) must be 2 movies with different titles but from the same year (e.g. The Martian 2015 and Bridge of Spies 2015). The 4th and 5th elements must be 2 different objects that represent the same movie (same title and same year). The remaining elements can be any movies you like. A hashCode() method. Use the following: public int hashCode() { return title.hashCode() + year; }

Interface FilmArchive Create an interface called FilmArchive that defines 2 methods: getSorted(), which takes no args and returns ArrayList. Implementations should return an array list whose members are unique according to deep equality, and sorted according to the criteria in Movies compareTo() method. add(), which takes one arg of type Movie and returns a boolean. If add() is called where the arg already appears in the film archive, the method should return false and otherwise do nothing; if the arg of add() does not yet appear in the archive, it should be added as described below and the method should return true.

3 implementing classes Create 3 classes, named ListFilmArchive, HashFilmArchive, and TreeFilmArchive, that implement the FilmArchive interface.

Class ListFilmArchive This class should extend ArrayList. In your add() method, check every movie in the array list for deep equality to the arg of add(). If you find a movie that equals() the arg, just return false; if you dont find one, add the arg to the array list and return true. Hint: you are overriding the add() method inherited from the ArrayList superclass. When you detect that the arg movie doesnt appear in the array list, you want to call the superclass version of add(). To do that, use something like this line: boolean reallyAdded = super.add(aMovie); super. in this overridden method tells Java please use the version of add in my superclass. For the getSorted() method, use a TreeSet to do the sorting. First construct a TreeSet, passing the ArrayList into the TreeSet constructor; since ListFilmArchive isa ArrayList, this is a reference to the ArrayList that you want to pass. Then construct and return a new ArrayList, passing the TreeSet into the ArrayList constructor; when that ArrayList is constructed, the movies in the TreeSet will be added to it one by one, in the TreeSets natural order, which is the order that you want. In other words, this long paragraph describes 2 simple lines of code.

Class HashFilmArchive This class should extend HashSet. Its ok to add movies to a HashSet because Movie has mutually compatible equals(), and hashCode() methods. For the add() method, first read the documentation for add() in the java.util.HashSet API page (https://docs.oracle.com/javase/8/docs/api/java/util/HashSet.html ). Convince yourself that this method does exactly what add() in HashFilmArchive should do. Since the inherited method is acceptable, you dont need to create add() in HashFilmArchive. (But you do need to understand why you dont need to). For the getSorted() method, do something similar to what you did in ListFilmArchive.

Class TreeFilmArchive This class should extend TreeSet. For the add() method, first read the documentation for add() in the API page for java.util.TreeSet (https://docs.oracle.com/javase/8/docs/api/java/util/TreeSet.html ). Convince yourself that this method does exactly what add() in TreeFilmArchive should do. Since the inherited method is acceptable, you dont need to create add() in TreeFilmArchive. For the getSorted() method, do something somewhat similar to, but simpler than, what you did in ListFilmArchive and HashFilmArchive. All you need to do is construct an ArrayList, passing this into the ArrayList ctor. Well, thats not all you need to do you also need to understand why it works.

Testing your 3 FilmArchive classes You already have test inputs: the array returned by Movie.getTestMovies(). Be sure that this array meets the requirements described above. To test the ListFilmArchive class, add the following main() method: public static void main(String[] args) { ListFilmArchive archive = new ListFilmArchive(); for (Movie m: Movie.getTestMovies()) archive.add(m); for (Movie m: archive) System.out.println(m); System.out.println("**************"); for (Movie m: archive.getSorted()) System.out.println(m); } If you get a compiler error on the line that prints out a row of stars, delete the quote signs and then type them back in. Some systems do weird things with smart quotes. Stupid smart quotes! Run ListFilmArchive as an app. Look at the number of movies that were printed out, and their order. Are these what you expected? To test HashFilmArchive, add the same main() to HashFilmArchive but change ListFilmArchive to HashFilmArchive. Then add the HashFilmArchive main() to TreeFilmArchive but change HashFilmArchive to TreeFilmArchive. This is a common way to test individual classes in Java: you give each class a main() method that tests just that class.

Lets do science Create the following class: package movies; public class HashAnalyzer { public static void main(String[] args) { HashFilmArchive archive = new HashFilmArchive(); for (int i=0; i<100000; i++) { archive.add(new Movie("Movie" + i, 2017)); if (i%1000 == 0) System.out.println(i); } System.out.println("DONE"); } } The main() method creates 100,000 fake movies and puts them into a HashFilmArchive. Every 1000 insertions, it prints out a message. When you run the app, the time interval between messages will give you feedback about time performance of the add() method of HashFilmArchive.

Create a second analyzer class called ListAnalyzer. It should be just like HashAnalyzer, except it should use a ListFilmArchive.